— Would you like to go and see the film with me this evening? 

— I am sorry, I can't because I _____ my homework. [ ]

A. does

B. did

C. am doing

D. has done

缺陷反射声能的大小，取决于（）

A.缺陷的尺寸

B.缺陷的类型

C.缺陷的形状和取向

D.以上全部