正常情况下，一个西瓜果实内含有种子的数目取决于[ ]

A．一朵花中有多少雌蕊

B．一个胚珠中有多少个卵细胞

C．一个雌蕊中有多少个子房

D．一个子房中有多少胚珠

Careful testing is necessary before any more experiments can continue with the exploring submarine.

A．needful

B．in need of

C．necessity

D．of necessity