I must have been a great _____ to my parents in those hard days, for I never failed to live up to their expectations.

A．achievement

B．comfort

C．disappointment

D．support

在作业地点悬挂（）的安全标志牌。

A.在此工作！

B.当心触电！

C.禁止合闸，有人工作！

D.止步，高压危险！