不及物动词做谓语时，若接宾语，则需接介词。如 He arrived at the hotel early. 如没有宾语，则不需接介词。如 He arrived early.
只有主谓结构就可以不加。比如 I slept.有宾语需要，就可以加。I am looking at her.
必须加介词。
