从经济法主体行为效果角度出发，可以将经济法主体的行为分为（）。

A.单方行为和双方行为

B.抽象行为和具体行为

C.积极行为和消极行为

D.自为行为和代理行为

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