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. they once grew D. once grew

优质解答

选 C.先行词是 those,可视为 those flowers 之省略.they once grew 前省略了关系代词 which.全句意为：这儿所养的花是由他们曾在森林里种植的花培养出来的.