prep sc 124 ..

124. The federal rules aimed at protecting human subjects of medical experiments were established to ensure that patients must be warned of potential risks and an independent panel would evaluate the experiment before it was conducted.

A. must be warned of potential risks and an independent panel would

B. must be warned of potential risks and that an independent panel

C. are warned about potential risks and that an independent panel

D. will be warned about potential risks and an independent panel would

E. would be warned of potential risks and that an independent panel would

A: must ， would不平行

B: must be不能省略；过去发生的事应该用would

C: 同上

D: 同上

E: correct

我对给出的解释不是很明白。。请牛牛帮我解释一下 

ensure and must when used together create redundancy.

"before it was conducted" shows that one event must have occurred prior to another event. Thus "would" is correct.

谢谢  。。