ag是拉丁动词agere的词干部分，意思相当于to do或to drive，意为做或驱使。agere的分词形式为actum, 因此，词根act与ag同源异形。

agent= ag- (= to do) + -ent (= person)-> person who does 办事者->n. person who works for another person or orgnizations 代理人

agency= ag- (= to do) + -ency (= the quality or state) -> the ability or place of doing business 办事的能力或场所 -> n. power or force which causes a result力量；作用

exact= ex- (= out) + act (= to drive) ->to drive out; driven out 逼出来；逼出来的 -> v. demand or obtain by force；adj. correct and without mistake 准确的；精准的

interact =inter- (= between) + act (= to do) -> to do between two things -> v. have an effect on each other 互相作用，互相影响