原题:A (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 herd 答案C Elephant emit low-frequency sounds, believed to be originate from a small area on their foreheads, that they may use
A:In grammer, the subject of “ believed......" is elephants, however it is no sense. Think it in a logic way, the subject should be sounds.
C:Elephant emit low-frequency sounds, believed to be originate from a small area on their foreheads, that they may use Now the meaning is right, " believed...."modifies sounds(就近修饰)