问题
选择题
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
答案
答案：C
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。