They had to knock the door down to get in.

他们不得不破门而入。

Knock the door before you enter.

进屋之前要先敲门。

You knock the door of my heart deeply.

你重重地扣开了我的心扉之门。

You should knock the door before you enter.

进门前你应先敲门。

I would knock the door, but you might be scared.

我想叩门，却怕你被我吓着。