请教一提PREP 的 SC

Rainbeauty

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
这个答案B 但D更好呀。。。
B的话木有体现出causal relationship

nemiah

Littering of orbits? 不对吧?

jameshzd

这题目的原意就没有 causal relationship， 就是liter 的来源于 the intentional discarding of A ，B and C。而不是因为这些垃圾 cause more litering，应该是人类丢垃圾cause more littering 吧。