—Most people said the film Let The Bullets Fly was wonderful _____ they watched it.

—I agree with them, and I like it very much!

A．before

B．if

C．since

D．after

选煤主要是利用煤和矸石的（）性质或物理化学性质的差别而进行分选的。

A、物理

B、生物

C、重量

D、大小