The reason ________he told us for his absence was ________ he was knocked down on the way

to school.[    ]

A. why; that  

B. why; why

C. which; that  

D. which; why

吊篮安装后应依次进行（）、空负荷试验。

A.防爆

B.绝缘性能

C.安全锁

D.安全绳