Recently documented examples of neurogenesis, the production of new brain cells, include the brain growing in mice when placed in a stimulating environment or neurons increasing in canaries that learn new songs.
A. the brain growing in mice when placed in a stimulating environment or neurons increasing in canaries that
B. mice whose brains grow when they are placed in a stimulating environment or canaries whose neurons increase when they
C. mice’s brains that grow when they are placed in a stimulating environment or canaries’ neurons that increase when they
D. the brain growth of mice when placed in a stimulating environment or the increase in canaries’ neurons when they
E. brain growth in mice that are placed in a stimulating environment or an increase in neurons in canaries that

OA (highlight the sentence to see the OA) = E

Doubt posted:

Can u please clarify to which word “that” points to ?
I think “that ” refers to either brain or mice.
1) If it refers to brain , it is likely refers to neurons in the 2nd part.( since both parts have parallel structure) If so how can neurons learn new songs ?
2) If it refers to mice , can animals or birds be referred using ” that”?