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

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。根据时间状语in the past decades在过去的几十年，说明一直到现在，并有可能继续持续下去，故用现在完成进行时。句意：在过去的几十年，由于全球变暖的原因，北极圈的海洋冰块一直在融合。故B正确。