在中国古代“家国一体”的社会中，忠孝观念源远流长，其源头是[ ]

A．宗法制

B．郡县制

C．君主专制

D．中央集权制

These batteries for electric cars, some scientists claim, are bound to be too heavy, too bulky and unable to store enough electricity.

A．clumsy

B．fussy

C．nasty

D．rusty