--Could you tell me ______________  for class this morning?

--I am sorry, Mrs. Lin. I got up so late that i couldn’t catch the first bus.

A．why were you late

B．why you are late

C．why are you late

D．why you were late

D型离心泵的总扬程是各单级扬程之（）。

A．差

B．和

C．乘积