Sentence Correction

A female meadow vole can produce a fresh litter of about five pups every three weeks if she chooses to breed at maximum speed, but they begin suppressing pup production from the moment they become conscious of nearby voles in excess.

A)they begin suppressing pup production from the moment they become conscious of nearby voles in excess
B)voles begin suppressing pup production from the moment they become conscious of an excess of nearby voles
C)the suppression of pup production begins by them from the moment they become conscious of nearby voles in excess
D) the moment they become conscious of an excess of nearby voles is when suppression of pup production begins
E)the moment voles become conscious of nearby voles in excess is when they begin suppressing pup production


Please explain reason to eliminate options

OAB

NandishSS wrote:A female meadow vole can produce a fresh litter of about five pups every three weeks if she chooses to breed at maximum speed, but they begin suppressing pup production from the moment they become conscious of nearby voles in excess.

A)they begin suppressing pup production from the moment they become conscious of nearby voles in excess
B)voles begin suppressing pup production from the moment they become conscious of an excess of nearby voles
C)the suppression of pup production begins by them from the moment they become conscious of nearby voles in excess
D) the moment they become conscious of an excess of nearby voles is when suppression of pup production begins
E)the moment voles become conscious of nearby voles in excess is when they begin suppressing pup production


Please explain reason to eliminate options

OAB

The first thing to look for is the subject verb agreement.
"A female vole" is singular, hence we cannot use "they"
Eliminate Options A, C and D

Out of B and E, Option E is unnecessarily wordy and awkward.
We do not need both "the moment" and "when"


Correct Option: B