大全179-RRDW

1.        Biologists believe that they have found one of the substances that tell individual genes both when to become active and when to remain quiescent in the earliest phases of an embryo’s development.

(A) tell individual genes both when to become active and when to remain

(B) tell individual genes both at which time they should become active or should remain

(C) tells individual genes both when to become active or remain

(D) tells individual genes both when to become active or when to remain（A）

(E) will tell an individual gene both about when it should become active and remain

就一个问题，为什么在这里 one of the substances that tell  而不是 tells 呢？

已经明白我 我尽问这种问题 Sigh  版主删了把 谢谢