The world's supplies of copper...a,have been gradually being exhaustedb,have gradually exhaustedc,are gradually exhaustedd,are being gradually exhausted

The world's supplies of copper...a,have been gradually being exhaustedb,have gradually exhaustedc,are gradually exhaustedd,are being gradually exhausted
The world's supplies of copper...
a,have been gradually being exhausted
b,have gradually exhausted
c,are gradually exhausted
d,are being gradually exhausted

The world's supplies of copper...a,have been gradually being exhaustedb,have gradually exhaustedc,are gradually exhaustedd,are being gradually exhausted
a.been和being重复
d.are和being重复
exhausted是一个持续的动作,固应用现在完成时,选B