Can you believe his reason for being absent from the class _____ he had to look after his sick mother at home?

A．while                 B．that                    C when                    D．as

下列配伍中属于相杀的是（）

A.黄芪配茯苓

B.麻黄配杏仁

C.生姜配生半夏

D.党参配黄芪

E.生姜配黄芩