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
网友回答
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。