我选C All of the plants now raised on farms have been developed from plants_that once grew_wild.

题目

我选C All of the plants now raised on farms have been developed from plants_that once grew_wild.
为什么不是once grown?而要有that?

答案

plants和grow是主用关系,植物自己长；
that做宾语从句主语,不能省略.