When he saw all his books _____ here and there on the floor, he knew that something terrible _____.

A．lying; must have happened

B．lie; must happen

C．lay; might have happened

D．had lain; could have happen

农村电网中的架空配电线路，主要由（）

A、电杆；

B、导线；

C、金具；

D、绝缘子；

E、拉线；

F、基础。