served

serve in, serve on

这两个短语都表示“在…任职”。它们的区别是：
serve in用于相对较大的范围,而serve on用于相对较小的单位与机构。

serve time, serve one's time

serve time的意思是“蹲过班房”或“吃了官司”; 而serve one's time则作“满期”或“见习期满”解。试比较:
The blackguard has served time for three years.
那坏蛋已坐了三年牢。
Tom has served his time.
汤姆已经转正了。

serve as, act as

这两个短语都可表示“充任,担任”。它们的区别是：
serve as多指长期供职; 而act as所指时间则相对较短。试比较:
He serves as manager and interpreter.
他兼任经理和口译。
She will act as my guide tomorrow.
明天她将给我作向导。