(请教)prep里的一道语法题!!

15. Recently documented examples of neurogenesis（神经形成）, 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 in 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

key:E

为什么D不对呢?

D: they不能指代canaries，因为 canaries' 是所有格