The reason ______ he was late again was that he was caught in traffic jam in the rush hour.[ ]

A. which        

B. in which

C. for which    

D. of which  

企业销售需要安装的商品时，若安装属于商品销售合同约定的卖方责任，则确认商品销售收入的时间应是()。

A.商品运到并开始安装时

B.商品安装完毕并检验合格时

C.购货方首次付款时

D.收到最后一笔销售货款时