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Biologists believe that they have found one of the [#permalink]
10 Apr 2007, 14:27
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179. 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 embryoâ€™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
It says "one of the substances", which is singular and hence tells will follow and not the tell, between C and D, D for parallelism.
The intent of the sentence is to say that "There are many substances that 'do something'. Scientists have found one of those substances. Even though the scientists found only substance, the action 'do something' is common across all the substances. Thus we need a plural form and I agree with others that A is the best answer.
Amardeep, here is another thread in which I had emphasized this.
It is clearly (A), -as already mentioned by buzzgaurav- because of the idiomatic expression '..both X and Y' and it is parallel 'when to become active and when to remain'.
I would suggest to post a clear explanation why something is right/wrong, so all of us can share your knowledge. Even if something is wrong, we all can learn a lot from the nasty traps. It is not useful to post A or B or C or D or E?! Best regards, thank you and cheers!