1 come in 意為“進來”,單獨使用,in 是副詞,后面不接名詞。
He was reading when I came in . 我進來時他在讀書。
She didn't allow the stranger to come in . 她不允許那個陌生人進來。
2 come into 意為“進來,進入”,into 是介詞,后面必須接名詞。
Please ring the bell before you come into the room. 進入房間前請先按門鈴。
We came into the hall one by one. 我們一個接一個進入大廳。
3 enter 也表示“進入”,正式用詞,為及物動詞,后面直接跟賓語。
The teacher entered the classroom with a book in his arm. 老師腋下挾著一本書走進教室。
She entered the university at the age of eighteen. 她18歲上了大學。