Prep 2-134, 请教,以前没问过

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

请问highlighted这部分的语法结构是什莫,百思不得其解。谢谢。

if ... and the absense(...) seems dangerous? 什莫意思?