Over the past decades sea ice in the Arctic as a result of global warming.A. had decrease

问题补充：

Over the past decades, sea ice in the Arctic as a result of global warming.

A. had decreased

B. decreased

C. has been decreasing

D. is decreasing

答案：

A. had decreased

B. decreased

C. has been decreasing

D. is decreasing

解析：考查时态。句中有Over the past decades谓语动词用现在完成时或现在完成进行时。