求助！Prep中关于 neurogenesis的题

Malimalihonmia

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.
Athe brain growing in mice when placed in a stimulating environment or neurons increasing in canaries that  分析A选项
Bmice whose brains grow when they are placed in a stimulating environment or canaries whose neurons increase when they  分析B选项
Cmice's brains that grow when they are placed in a stimulating environment or canaries' neurons that increase when they  分析C选项
Dthe brain growth in mice when placed in a stimulating environment or the increase in canaries' neurons when they  分析D选项
Ebrain growth in mice that are placed in a stimulating environment or an increase in neurons in canaries that  分析E选项

答案是E
但是 brain growth in mice为什么没有冠词啊？