关于use as的用法，求助

jasonwzhan

在大全987-174中

1. Believed to originate from a small area on their foreheads, elephants emit low-frequency sounds that may be used as a secret language to communicate with other members of the herd.

(A) Believed to originate from a small area on their foreheads, elephants emit low-frequency sounds that may be used

(B) Elephants emit low-frequency sounds that are believed to originate from a small area on their foreheads, and they may use this

(C) Elephants emit low-frequency sounds, believed to originate from a small area on their foreheads, that they may use

(D) Originating, it is believed, from a small area on their foreheads; elephants emit low-frequency sounds they may use（C）

(E) Originating, it is believed, from a small area on their foreheads, low-frequency sounds are emitted by elephants that may be used.

C项是正确答案，但是对于C项末尾的they may use，和后面的as连起来好别扭啊。

这个they应该指elephant吧，莫非use as中间省略了such sounds?

对省略的尺度实在是把握不助，use as 可以这样用吗？盼nn解答，谢谢！

xizzhu

use something as something   is a phrase.