—Hello, John, how are you? Are you busy now?

—Not really. I ________ my report. And now I am watching an American movie on TV.[ ]

A. finished  

B. have finished

C. had finished  

D. have been finishing

钢板探伤中可根据（）判断缺陷是否存在。

A.参考回波减弱

B.缺陷回波

C.底波

D.以上都对