885/13-15.22

catherine11

15.    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
(E) will tell an individual gene both about when it should become active and remain

请问这里为什么用tell 而不用tells? The answer is A!

22.    In its most recent approach, the comet Crommelin passed the Earth at about the same distance and in about the same position, some 25 degrees above the horizon, that Halley’s comet will pass the next time it appears.
(A) that Halley’s comet will pass
(B) that Halley’s comet is to be passing
(C) as Halley’s comet
(D) as will Halley’s comet
(E) as Halley’s comet will do

Why choose D rahter than E?

nina23

1)that指的是substances

2）比较句子时只需要补出助动词即可