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：考察时态。本题的关键是前面的时间状语In the past decades。只要出现“in the past/last+一段时间”，都要和现在完成时连用。句意：在过去的几十年里，由于全球变暖，北极的海冰一直都在融化。B项的现在完成进行时表示从过去开始一直延续到现在的情况。这一情况符合题意。