It is estimated that the price of a personal computer ______ by a_英语解答

It is estimated that the price of a personal computer ______ by an average of 25% a year since 1990.
A.fell B.had fallen
C.is falling D.has fallen
选哪个,为什么?

人气：188 ℃　时间：2020-04-07 00:39:37

解答

D
since是很典型的完成时标志,所以在BD里选
主句是一般现在时,所以不用B