每个子女都含有父母双亲的遗传物质，母亲的遗传物质是通过下列哪种细胞传递给子女的[ ]

A．脐带

B．卵细胞

C．受精卵

D．子宫内膜

I can't give my son the leading position.________, he is too young；secondly, I want Mr Smith to

have the job. [ ]

A. After all  

B. For example

C. In the end  

D. To begin with