百思不得其解一道GMAT GWD SC题...

题目

百思不得其解一道GMAT GWD SC题...
整个句子都划线了.
a.When an active tooth in the shark's jaws is lost or worn down,many spare teeth lie in seemingly limitless reserve,each of which are ready to slide into the appropriate position.
e.In the shark's jaws,many spare teeth lie in seemingly limitless reserve,each one ready to slide into the appropriate position whenever an active tooth is lost or worn down.
each of which明显要用单数啊,怎么会选a,而且句子意思when tooth is lost,many spare teeth lie in...感觉好像是牙齿掉了,其它的牙齿才lie in一样.

答案

E,主句是：many spare teeth lie in seemingly limitless reserve,这里有一个地点状语从句in the shark’s jaws修饰lie,逻辑主语是lie的主语many spare teeth .从句是：each one ready to slide into the appropriat...