you should knock at the door before you the room.为什么用enter而不

enter=go into ,动词,意思是：进入;进来 ,后面直接跟进入的地点,不需要另外加介词into.
When you enter a place such as a room or building,you go into it or come into it.
例句：
1、He entered the room briskly and stood near the door...他轻快地走进屋里,站在门边.
2、Before entering the bathroom,he emptied his dirty laundry into the hamper...进浴室前,他把脏衣服全都放进洗衣筐里.
3、As soon as I entered,they stopped and turned my way.我一进去,他们就停下来转身朝向我.

enter 、into 都有进入的意思，区别是enter是实义动词，而into是介词，enter into 连用就重复了，而且句子中缺少的是一个实义动词，强调的是进入这个动作，而不是进入这个过程，综上所述不能用enter into。希望你满意！

enter是进入的意思，你可以把它看做一个及物动词，相当于go into.

she should at the door ……（with）