by bus是介词短语, 修饰谓语, take bus 作谓语
by bus表示方式作副词用 i came here by bus
take a bus表示动作啊. i will take a bus to go there
by bus 作状语用
we went to school by bus.
take bus :take是谓语 bus是宾语。
we will take a bus.
by bus:介词短语
take bus:动词短语
例:go to work by bus
take a bus to my workplace