good question and i know you are intimited by the migrain.
the subject of the verb "cost" is not migrain.
the subject is "who". who refers to those migrain afflicted 18 mil people.

(B) year and thus cost the nation $50 billion in medical expenses and lost

will explain..

shouldn't it be "costs" to agree in number with noun (Migraine)
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Migraine, the most debilitating common form of headache, afflicts perhaps 18 million Americans, who collectively lose 64 million workdays a year, and they cost the nation $50 billion in medical expenses and lost work time.

(A) year, and they cost the nation $50 billion in medical expenses and lost - they can refer to 'Americans' or 'workdays'

(B) year and thus cost the nation $50 billion in medical expenses and lost - thus is correct here. Americans lose workdays and thus (therefore) cost the nation $50 billion (CORRECT)

(C) year, so as to cost the nation $50 billion in medical expenses and lost - 'so as to' is almost always incorrect in GMAT

(D) year that costs the nation $50 billion in lost medical expenses and - 'that' refers to year which is incorrect. The loss of $64 billion dollars is because of the loss of workdays and not because of 'year'

(E) year, which thus cost the nation $50 billion in lost medical expenses and - 'which incorrectly refers to 'year'

(A) year, and they cost the nation $50 billion in medical expenses and lost
", and they" makes the construction awkwrd. If they refers to the Americans then there is no need for the comma... Also, "they" should not be used... Look at the structure: "...afflicts blah blah Americans, who lose blah blah in a year and [they] cost.." NOT PARALLEL..

(B) year and thus cost the nation $50 billion in medical expenses and lost
CORRECT. "who collectivelu lose blah blah and thus cost the nation blah blah" simply modifies Americans

(C) year, so as to cost the nation $50 billion in medical expenses and lost
"Migraine afflicts a number of Americans, who are blah blah in a year, so as to cost the nation..." changes the meaning by making the cost look intentional...

(D) year that costs the nation $50 billion in lost medical expenses and
misplaced modifier by touch-rule

(E) year, which thus cost the nation $50 billion in lost medical expenses and
"who collectively lose 64 million workdays a year, which costs..." is OUT because of misplaced modifier.

Answer: B

(A) year, and they cost the nation $50 billion in medical expenses and lost - Wrong: 1) Pronoun Ambiguity 2) Parallelism issue

(B) year and thus cost the nation $50 billion in medical expenses and lost - Correct

(C) year, so as to cost the nation $50 billion in medical expenses and lost - Wrong: 1) Meaning issue

(D) year that costs the nation $50 billion in lost medical expenses and - Wrong: 2 modifier issues

(E) year, which thus cost the nation $50 billion in lost medical expenses and - Wrong: 2 modifier issues

(A) year, and they cost the nation $50 billion in medical expenses and lost

(B) year and thus cost the nation $50 billion in medical expenses and lost

(C) year, so as to cost the nation $50 billion in medical expenses and lost

(D) year that costs the nation $50 billion in lost medical expenses and

(E) year, which thus cost the nation $50 billion in lost medical expenses and

lost medical expenses vs Medical expenses

Eliminate D and E

They is ambigious. Eliminate A

So as to change meaning, there is no indirect cause and effect.

Hence B
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This question just seems pretty off in terms of meaning. Fundamentally, it is the disease that costs the nation money and lost workday, not the people. The correct answer C's meaning seems off. Honestly, I feel like "so as to" kinda works, but it involves too much about intention/purpose, which is not what the disease is intentionally doing.

Migraine, the most debilitating common form of headache, afflicts perhaps 18 million Americans, who collectively lose 64 million workdays a year, and they cost the nation $50 billion in medical expenses and lost work time.

Meaning Analysis: Migraine (which is a common form of headache) affects 18M Americans. These "affected" Americans lose 64 million work days and as a result of them losing so many work days, they cost the nation $50 billion in the form of (1) medical expenses and (2) work time that they lose out on

Sentence structure:

Migraine (Subject)
,the most debilitating common form of headache, (Modifier modifying the noun "Migraine") (notice the modifier is in a COMMA PAIR)
afflicts (Verb)
perhaps 18 million Americans (modifier - gives additional information about the verb)
,who collectively lose 64 million workdays a year, (Relative noun modifier modifying "Americans") (DC - "who" Subject ; "lose" - Verb)
and (Parallelism marker)
they (Subject)
cost (Verb)
the nation $50 billion in medical expenses (Additional information about cost)
and (parallelism marker)
lost work time. (second entity of the parallel list)

Error Analysis:

(A) year, and they cost the nation $50 billion in medical expenses and lost - Incorrect We want to convey that due to the loss of 64 million work days the nation incurs $50B. But by starting an IC we are conveying two separate ideas. This sentence now conveys that
(1) The 18M affected Americans lose 64M word days and
(2) the 18M affected Americans cost the nation $50B.

As we can see, the intended "cause and effect" relationship is not correctly conveyed

B) year and thus cost the nation $50 billion in medical expenses and lost - Correct By using "thus" we are stating the result of "the loss of 64M work days". Note - The verb "Cost" refers back to the plural subject "who" that modifies the plural noun "Americans".

We also see the correct Parallel structure. in medical expenses and lost work time . Here "in" is not repeated after "work time" and that is alright as ellipses is in play

C) year, so as to cost the nation $50 billion in medical expenses and lost - Incorrect.
So as to means so that. Thus we are now saying that they lose 64M work days so that they cost the nation $50B and this is completely illogical.

(D) year that costs the nation $50 billion in lost medical expenses and - Incorrect. the Nation loses $50B in "medical expenses" There is no such thing as "lost medical expenses". The only thing that is lost is the work days!

Note - I believe the usage of "that" is alright out here."That" can very well modify the preceding clause "who collectively lose 64 million workdays a year" thus stating that Americans lose 64M workdays a year and thus costs the nation $50B

(E) year, which thus cost the nation $50 billion in lost medical expenses and. Incorrect. Same error of (D) "lost medical expenses" + "which" may seem to refer to "year" and that would make the sentence illogical.


Correct Choice: (B)

HI GMATNinja, generis, AndrewN

In Option A, Pronoun ambiguity is not a hard rule eliminate so wanted to check, here Isn't they logically refers 64 million workdays ? How to eliminate A?
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Hi Nandish

"They" in option (A) could logically refer either to "64 million workdays" or to "18 million Americans". Hence, there is an ambiguity about the antecedent of "they". This is clear error.

I would always be wary of eliminating an answer option solely based on pronoun ambiguity (unless I am able to find another answer option with no ambiguity and no other errors). In this case, however, we have another issue with option (A).

"and" following "year" shows the existence of a list that must obey parallelism. However, "who collectively lose..." and "they cost the nation..." are not parallel, with one being a relative pronoun and other a simple pronoun. If we begin the list after "who", then "collectively lose" is a verb form which is not parallel to "they cost the nation..." either. Basis the above, we can eliminate option (A).

Hope this helps.
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Hello, NandishSS. I agree with what CrackVerbalGMAT has posted above. Speaking to your concern about pronoun ambiguity, no, it is not in itself a death sentence if an answer choice incorporates less-than-100-percent clear pronouns. Just do not lose sight of the five options presented. If a safer, harder-to-argue against alternative presents itself, as occurs in (B) above, then choose that option instead, every time. Watch the correct answers come rolling in. You may even think in terms of caution signs against different answer choices in the first pass, particularly if you cannot spot any clear violations. Take (A) and (B), for instance:



Now, between the two answer choices, you should ask yourself whether it is necessary to turn the sentence into a compound sentence. Is the comma warranted? Also, what about they? If it is not entirely clear, then you have two caution signs in that answer. In (B), though, the lack of a comma indicates two parallel elements, and lose and cost match up perfectly. Between the two answer choices, (B) is the clear winner.

I hope that helps. Thank you for thinking to ask me about this one.

- Andrew

Thank you CrackVerbalGMAT and AndrewN for the clarification
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There is something confusing about the logic of the sentence. Would be grateful if someone could clarify.

Migraine affects 18mn people.
18mn people collectively lose 64 mn workdays
Losing 64mn workdays thus costs the nation 50bn in medical expenses and lost work time.

How can losing 64mn workdays cost in medical expenses? I can understand lost work time