Official Solution:

Whereas in mammals the heart, which has four chambers, two ventricles and two atria, delivers oxygenated blood to the organs by one channel while the other directs blood to the lungs for re-oxygenation, the reptiles have three-chambered hearts with two ventricles and only one atrium.

A. in mammals the heart, which has four chambers, two ventricles and two atria, delivers oxygenated blood to the organs by one channel while the other directs blood to the lungs for re-oxygenation, the reptiles have three-chambered hearts with
B. in mammals the heart has four chambers, two ventricles and two atria, and delivers oxygenated blood to the organs by one channel while directs blood to the lungs for re-oxygenation by another, the heart in reptiles has three chambers,
C. the mammalian heart, consisting of four chambers, two ventricles and two atria, delivers oxygenated blood to the organs by one channel, while the other directs blood to the lungs for re-oxygenation, the reptilian heart has three chambers,
D. the mammals have hearts consisting of four chambers, two ventricles and two atria, which deliver oxygenated blood to the organs by one channel, while direct blood to the lungs for re-oxygenation by another, the reptiles’ hearts have three chambers,
E. the mammals have hearts consisting of four chambers, two ventricles and two atria, delivering oxygenated blood to the organs by one channel, while directing blood to the lungs for re-oxygenation by another, the reptiles’ hearts have three-chambers,


A. The contrast using whereas must have two parallel elements. The heart (in mammals) is wrongly contrasted with the reptiles. Moreover, the contrast using while too must have two parallel elements. Faulty parallelism exists between delivers oxygenated blood to the organs by one channel and the other directs blood… .

B. Correct. The heart (in mammals) is correctly contrasted with the heart in reptiles.
Parallelism is maintained between delivers oxygenated blood to the organs by one channel and directs blood to the lungs for re-oxygenation by another.
C. The construction the mammalian heart… …..delivers oxygenated blood is wrongly contrasted with the reptilian heart has 3 chambers – the contrast is wrongly established between delivering blood and having 3 chambers. Faulty parallelism exists between delivers oxygenated blood to the organs by one channel and the other directs blood… .

D. The contrast is wrongly established between the mammals and the reptiles’ hearts. The modifier which deliver oxygenated….. by another wrongly refers to atria.

E. The contrast is wrongly established between the mammals and the reptiles’ hearts. The present participle (-ing) modifier delivering oxygenated blood………by another seems to refer incorrectly to the subject (the mammals) of the preceding clause – the mammals do not deliver oxygenated blood, their hearts do.


Answer: B
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Whereas in mammals the heart, which has four chambers, two ventricles and two atria, delivers oxygenated blood to the organs by one channel while the other directs blood to the lungs for re-oxygenation, the reptiles have three-chambered hearts with two ventricles and only one atrium.

Structure: Whereas X, Y
Y = .........with two ventricles and only one atrium.

A. in mammals the heart, which has four chambers, two ventricles and two atria, delivers oxygenated blood to the organs by one channel while the other directs blood to the lungs for re-oxygenation, the reptiles have three-chambered hearts ==> not parallel in term of X & Y

B. in mammals the heart has four chambers, two ventricles and two atria, and delivers oxygenated blood to the organs by one channel while directs blood to the lungs for re-oxygenation by another, the heart in reptiles has three chambers, =>Correct, parallel structure: Whereas [mammals heart] has ... and delivers...., [reptiles heart] has...

C. the mammalian heart, consisting of four chambers, two ventricles and two atria, delivers oxygenated blood to the organs by one channel, while the other directs blood to the lungs for re-oxygenation, the reptilian heart has three chambers, ==> to which "the other" refer? Atria?

D. the mammals have hearts consisting of four chambers, two ventricles and two atria, which deliver oxygenated blood to the organs by one channel, while direct blood to the lungs for re-oxygenation by another, the reptiles’ hearts have three chambers, ==> to which "which" refer to?, also, parallel structure in X & Y

E. the mammals have hearts consisting of four chambers, two ventricles and two atria, delivering oxygenated blood to the organs by one channel, while directing blood to the lungs for re-oxygenation by another, the reptiles’ hearts have three-chambers, ==> to which "delivering oxygenated blood to the organs by one channel" modify?

I think this is a poor-quality question and I don't agree with the explanation. Answer B cannot be correct. Answer choice B compares mammals to to the heart in reptiles.

I think this is a poor-quality question and I don't agree with the explanation. It compares two different things: "mammals" and "the heart"

No, your point is not correct. It is very clear that "the heart IN mammal" and " the heart IN reptiles" are compared. Putting "IN mammals" before "the heart" does not make "mammals" the first item being compared. Both of you have just fallen into a trap intentionally laid by the question writer.

My issue with the answer here does not arise from comparison (I think the placement of "in mammals the heart" vs "the heart in reptiles" is somewhat clear in meaning) but instead with subject/verb agreement.

B says "the heart... delivers oxygenated blood to the organs by one channel WHILE DIRECTS BLOOD to the lungs..."

This is clearly not correct in my opinion. If it said "and directs" it would make more sense because those are the two functions that the heart performs and "directs" is parallel with "delivers".

Anyone care to correct me here if my reasoning is incorrect?

"While" is a conjunction that is used to depict that two actions happen simultaneously. The sentence implies that the
"delivery of oxygenated blood to the organs" and "the directing of blood to the lungs for re-oxygenation" happens simultaneously. Therefore use of "while" is alright.

I am not clear why you see an S/V disagreement - the subject for the singular verbs "delivers", "depicts" and "has" is singular "the heart".

Whereas in mammals the heart has four chambers, two ventricles and two atria, and delivers oxygenated blood to the organs by one channel while directs blood to the lungs for re-oxygenation by another, the heart in reptiles has three chambers, with two ventricles and only one atrium.

Is the usage of with correct here?
Please clarify.
Thanks.

Yes it is alright. Compare with the following example:
I have a striped shirt with one pocket and six buttons.

Actually BC can be quickly shortlisted first.
But in c, ... the mammalian heart, consisting of four chambers, two ventricles and two atria, delivers oxygenated blood to the organs by one channel, while the other directs blood to the lungs for re-oxygenation, the reptilian heart has three chambers,

This is wrong... heart and value of heart are not parallel. This is corrected in B.

in mammals the heart has four chambers, two ventricles and two atria, and delivers oxygenated blood to the organs by one channel while directs blood to the lungs for re-oxygenation by another, the heart in reptiles has three chambers,

Has and directs are verbs that are parallel.

Am i right in my thinking? experts plz comment.

It is not clear what you mean my "value of heart". Please elaborate.

The parallelism in the correct option B is not between "has" and "directs", but between "delivers" and "directs". The first "has" (The heart in mammals has) is parallel to the second "has" (The heart in reptiles has).

Option C is wrong because of wrong parallelism between "delivers" (The mammalian heart delivers) and "has" (The reptilian heart has). The OE elaborates this point further.

I agree. But the sentence in question has a slightly different structure.
Here, the ventricles are the chambers themselves.
I find the sentence analogous to:
I have 3 vehicles,with two cars and only one bicycle.

IS it right??
thanks.

You are right - the usage given in option B (and the example you pointed out) is incorrect - the preposition "with" should not be there. We have modified the question to take care of this issue.

Thank you for your inputs.

I think this is a poor-quality question and I don't agree with the explanation. the language in the correct answer "...delivers oxygenated blood to the organs by one channel while directs blood to the lungs.." is poor. The "while directs" makes no sense.

This question is a stunning / beauty. Stupendously testing the Parallelism grammar. This is one question where Parallelism and Logic go hand in hand together to reach the destined answer B.
Thank you for such an awesome question. I had this question just a while ago when i was doing my GMATClub test.

I think this is a poor-quality question and I don't agree with the explanation. I believe answer "B" should be corrected. The section "by one channel while directs blood to the lungs" should actually read "by one channel while *directing* blood to the lungs". Besides this error the answer is fine.

I think this is a poor-quality question and I don't agree with the explanation. really of poor quality

I too felt the same when i read the question for 1st time. But when i read for the 2nd time, i understood it

I agree that this is a low quality question. When you remove the superfluous details of the sentence it becomes clear that the 'correct' answer B is grammatically incorrect.

Whereas in mammals the heart has X, ..., and delivers Y while directs blood to the lungs for re-oxygenation by another, the heart in reptiles has Z.

Should be while directing blood.