Since the start of the space age, more and more littering has occurred in orbits near Earth, often because the intentional discarding of lens caps, packing material, fuel tanks, and payload covers.
(A) more and more littering has occurred in orbits near Earth, often because
(B) orbits near Earth have become more and more littered, often from
(C) orbits near Earth became littered more and more, often resulting from
(D) there have been more and more littering of orbits near Earth, often because of
(E) there had been littering more and more of orbits near Earth, often with
答案是B
可是B不应该是have became么。。。 作者: mogu724 时间: 2013-10-29 00:01
顶。。。。。。。。。。。。。。。作者: saintsun 时间: 2013-10-30 15:57
have became是什么？过去分词就是become