He asked his father why he was not able to hatch chickens hens could.A. howeverB. whileC.

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A. however
(答案→)B. while
C. as
D. although
解析：
试题分析:句意：他问他父亲他为什么不能孵小鸡而母鸡却能。A然而，不管，不论；B然而；C由于，当……时；D尽管。根据句意可知前后句内容是转折关系，故选B。