–Why didn’t you go to the movie last night?

_ Because I _____ the film before..

A．was seeing

B．saw

C．have seen

D． had seen

具有直接电离作用的粒子是（）。

A.α粒子和中子

B.β粒子和光子

C.α粒子和β粒子

D.光子

E.中子