Many air flights _________because of the eruption of the volcano, in _______case, many passengers had no choice but to take a train.

A．had been cancelled; which

B．have been cancelled; what

C．had been canceling; that

D．have been canceling; where

睾丸在胚胎哪个时期开始下降到阴囊（）。

A.3个月

B.4个月

C.4～5个月

D.7～8个月

E.出生前后