题目内容：

All of the flowers now raised here have developed from those ______ in the forest.
A.once they grew B.they grew once C.that once grew D.once grew
为什么不选C呢?

优质解答

that指代不可数名词和单数可数名词(如是复数,用those).
因为题目中已出现those指代all of the flowers,因此后面直接是once grew.
希望你可以明白