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

Q:我认为因为C中believed to 前有,分开,导致C中的believed to 的逻辑主语应为Elephants ,而不是 sounds,不符合逻辑,故我认为E对,E中IT指代整句的主语sounds ,弥补了C中的逻辑错误.

E后面的that may be used修饰对象是elephant，不合逻辑啊！

我觉得-ed分词短语修饰对象有一个就近原则，这里就是就近修饰sounds，而不是elephant.

我还有问题C中的THAT前有","分割,即THAT修饰非限制性定语从句,这不是不符合语法规则吗?

完全同意！C的表达最为清晰！