John has great singing _____, but to become a real singer, he needs a lot of necessary training and practice. [ ]

A. privilege

B. potential

C. promotion

D. possibility

下列各句中“乃”表示判断的一项是(　　)

A．今君乃亡赵走燕。

B．若事之不济，此乃天也。

C．旬乃还第。

D．今其智乃反不能及。