IMO A

that is incorrect when comparing with plural - rats, B, C are out.
E is out due to unnecessary use of possessive in rat's and change of tense to present progressive.
D is out due to incorrect use of which, which refers to nostrils and not the system

Although common moles cannot see, they possess a remarkable stereo system of olfactory awareness resembling those of rats, a system that combines smells accessed independently by both nostrils and makes the mole highly efficient at tracking an odor to its source.

A) resembling those of rats, a system that combines smells accessed independently by both nostrils and makes
It is incorrect to use plural THOSE for singular STEREO System. Hence Incorrect

B) that resembles that of rats and combines smells accessed independently by both nostrils, which make
Use of first THAT is incorrect since such use means that AWARENESS resembles STEREO SYSTEM of Rats, an Illogical comparison. It's not the NOSTRILS but the STEREO SYSTEM that makes mole highly efficient. Moreover, use of AND is also incorrect. Hence Incorrect

C) resembling that of rats and combining smells accessed independently by both nostrils that make
It's not the NOSTRILS but the STEREO SYSTEM that makes mole highly efficient. Moreover, use of AND is also incorrect. Hence Incorrect

D) that resembles those of rats and combines smells accessed independently by both nostrils, which makes
It is incorrect to use plural THOSE for singular STEREO System. It's not the NOSTRILS but the STEREO SYSTEM that makes mole highly efficient. Moreover, use of AND is also incorrect. Hence Incorrect

E) resembling a rat's, a system combining smells accessed independently by both nostrils and making
CORRECT

Here we are comparing a remarkable stereo system of moles with the system of rats. Hence THAT must be used instead of THOSE; hence A is wrong.
Among other choices B,C,D use which/that in ambiguous manner and hence the options are incorrect.
Though option E uses possessive the option expresses the meaning clearly and the correct option among the available choices.
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Can we have the OA

I went with B.
" Those of rats" is wrong as we are comparing remarkable system of ....awareness , hence we need that , a singular entity.
among the remaining options .
We need make instead of makes because " olfactory system and combines " make a plural subject. hence D is out.
among the remaining options I feel E's comparison is not clear.
Between B and C went with B. Though I am not sure of the double use of " THAT "
can we please have the OA .
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As I have pointed out, the RSSing.com posts carry neither the OA nor OE. But, the consensus seems to be E
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Although common moles cannot see, they possess a remarkable stereo system of olfactory awareness resembling those of rats, a system that combines smells accessed independently by both nostrils and makes the mole highly efficient at tracking an odor to its source.

A) resembling those of rats, a system that combines smells accessed independently by both nostrils and makes - INCORRECT
B) that resembles that of rats and combines smells accessed independently by both nostrils, which make - INCORRECT - 'that of' singular; 'which make' singular again
C) resembling that of rats and combining smells accessed independently by both nostrils that make - INCORRECT retains the singular and plural error
D) that resembles those of rats and combines smells accessed independently by both nostrils, which makes - I can understand consensus on E - but the sentence with this makes meaning clearer too. "they (MOLES) possess a remarkable stereo system ....[b] that RESEMBLES THOSE of rats ('those' for rats being plural) and combines.....which makes the mole highly efficient at tracking an odor to its source. Also, 'which' is not incorrect - it/ which are used for non -human entities. Ex: a rabbit has big ears which makes it efficient at listening to vibrations. If we check with the "stereo system that has...abcd... which makes ..highly efficient.[/b]
E) resembling a rat's, a system combining smells accessed independently by both nostrils and making - Seems a little awkward in sentence construction --> "(MOLES) possess a remarkable stereo system ....[b] resembling a rat's (to me, you cannot compare MOLE(S) plural to singular rat's- also rat's is left hanging) a system combining x and y making (there seems to be some repetition and clause issue - there should have been a semi colon before as its a complete sentence) the mole highly efficient at tracking an odor to its source. [/b]

D seems more correct to me. Would appreciate any expert opinion!

Official Explanation from egmat :
Error Analysis
The plural pronoun “those” does not agree in number with the singular antecedent “system”.

Note that the noun + noun modifier “a system that…” is used correctly in this sentence to describe the olfactory system of moles.

Answer Choices
A ) resembling those of rats, a system that combines smells accessed independently by both nostrils and makes

Incorrect:

This choice has the errors pointed out in the error analysis.

B) that resembles that of rats and combines smells accessed independently by both nostrils, which make

Incorrect:

The relative pronoun modifier “which” incorrectly modifies the preceding noun “nostrils”. It is the entire system that makes the moles efficient at tracking odors.

C) resembling that of rats and combining smells accessed independently by both nostrils that make

Incorrect:

Like choice B, this choice also has a modifier error since the relative pronoun modifier “that” incorrectly modifies the preceding noun “nostrils”.

D) that resembles those of rats and combines smells accessed independently by both nostrils, which makes

Incorrect:

1) This choice has the same comparison error as in choice A.

2) The relative pronoun modifier “which” should logically refer to the action “combines”. This usage is grammatically incorrect since a pronoun can refer only to a noun.

E) resembling a rat’s, a system combining smells accessed independently by both nostrils and making

Correct:

This choice corrects the only error of the original sentence by removing “those of”. The possessive form “rat’s” refers to “a rat’s ‘stereo’ system”.

A) resembling those of rats, a system that combines smells accessed independently by both nostrils and makes
It is incorrect to use plural THOSE for singular STEREO System.
INCORRECT

E) resembling a rat's, a system combining smells accessed independently by both nostrils and making
Use of THAT is correct and combining and making are parallel.
CORRECT

How can you compare Moles' (plural) system to a rat's (singular) system in option E?