IMO A... wats the OA?
Its subjunctive mode... hence, singular noun drug will have undergo instead of undergoes

IMO: A, as well!

This is a subjunctive modifier problem therefore, undergo is the right usage......

zaarathelab wrote:If a drug that is already on the market has the potential to help adults and children who have the same disease,or if it is widely used in children and the absence of labeling seems dangerous, the FDA can require that the drug undergo pediatric study.

(A) that the drug undergo
(B) that the drug undergoes
(C) that the drug is to undergo
(D) the drug undergoing
(E) the drug to have to undergo

Command subjunctive structure

1. ---------- Bossy verb + that + subject + command subjunctive
I require that he be here.

The other way is to make the subject of the subordinate clause as the object of the main clause by using "to"

2. ----------- Bossy verb + to + object + command subjunctive
I require him to be here.

Both are acceptable form for command subjunctive.

Please note that this two usage are interchangable but at times certain verb dont take "to" - unidiomatic usage and at times meaning demands a particular construction.

So you know why A is the answer as rest all violates the given structure of command subjunctive.

Hope this helps

+1 for A.

I used <Command Subjunctive> + that + <base form of verb>

Crick