1.
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
OA is B
请问 B里面的 often from到底是谁的modifier? 我找不到可以被他修饰的Noun啊.
如果 说often from是做adverbial modifier，它修饰的动词是哪一个？ 这算是那一种结构have become...., from...? | 
