大全987-174

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 怎么看都不对.  盼望 nn 解答.   我选了B.

174, 补充-177

按照believed的用法只有C。B中that are 多余，this不能单独指代，并且主从改变。

thanks carolhide, your explaination really makes sense.  

,that 这样的用法真的可以吗？？从来没见过啊

wordd的语法纠正就觉得是错的……那个小绿波浪阿~~

如果可以这么用肯定是c没问题了