Sentence Correction

Is that the issue here? I dont think its the "the" in option 4. Thanks.

What is the answer for this? Can someone explain this?

A - ing (present continous) form is incorrect. it shows that the brain is still growing & the neurons r still increasing.
B - they doesnot have a clear antecedant.
C - they represents mice's brains whereas it is the mice that r placed in stimulating environment.
D - (second half of the underlined portion) they refers to neurons whereas it should refer to canaries.

Hence IMO E.


Thanks!

ahh..good explanation. Thanks.