In the past decades sea ice in the Arctic as a result of global warming.A. had meltedB. h

问题补充：

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

A. had melted

B. has been melting

C. melted

D. is melting

答案：

A. had melted

(答案→)B. has been melting

C. melted

D. is melting

解析：考查时态。In the past decades通常都与现在完成时连用或者现在完成进行时连用。句意：在过去的几十年里，由于全球变暖，北极海冰一直在融化。