麦积山石窟开始营建于（）。
A.前秦
B.后秦
C.前凉
D.西魏
参考答案：B
— _____________ is your father?
— He is a bus driver.[ ]
A. Which
B. Who
C. Where
D. What
a2bm与-a2b是同类项，则m=______．
