isisalaska wrote: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 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

Correct is A
I though one of the substances is singular...

... one of the substances that tell

I hope that is sufficient
detailed explanation will follow if you want it...

Do you mind an explanation? thanks

isisalaska wrote: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 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

Correct is A
I though one of the substances is singular...

there are several substances that describe (tell) individual genes when to....

& biologists found one of them (substances )

that means it is not the only one that tells individual genes...
that could change the meaning of the sentence & in fact makes a sentence meaningless
Reason: one of the substances... need to have some support, as: which substances /what they do etc... otherwise author wouldnt have called it as "one of the... "in the first place...

Take a simple sentence:
Johny thinks that his one of the pens is stolen
& heres one more

Johny believes that his one the pens that are kept in drawer is stolen.


Johny is dazed and confused

Ah!!!!!!! thanks!

Also guyzz!!! dont u feel that the sentence is in the subjunctive!!! Use of the word believe and the use of the verb 'that' in the sentence signifies that the sentence is in the subjunctive.
Please mark me if I am wrong....

isisalaska wrote: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 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

Correct is A
I though one of the substances is singular...

In B, C and D, BOTH at...OR should (in B), BOTH when...OR remain (in C), and OTH when...OR when are unidiomatic. The correct idiom is BOTH X AND Y. Eliminate B, C and D.

In E, both ABOUT and REMAIN is not parallel. Eliminate E.

The correct answer is A.

There is no subjunctive mood here. The subjunctive mood would be warranted if the biologists believed that they WOULD FIND one of the substances. But what the biologists believe is offered as FACT: that they HAVE FOUND one of the substances.