题目

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：C 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。下列河流中，结冰期最长的是 （ ）A.长江 B.黄河 C.黑龙江 D.珠江