The first use of atomic weapon(原子弹)was in 1945, and their power _________ increased ever since．

A.is

B.was

C.has been

D.had been

答案及解析： C

解析：

本题考查动词的时态。ever since从那以后，指从1945以后到现在，所以句子应该用现在完成时态。