研磨薄形零件，拱曲变形的主要原因是（）。

A.磨料太粗 

B.磨料太细 

C.速度太快 

D.研磨剂涂得太厚

Kate, have you ______ the party It's time to go now.

A．heard from


B．been interesting in
C．waited for


D．got ready for