door與介詞和動詞的搭配問題
1. 若表示“在門口”，通常與介詞at搭配。如：
Someone’s knocking at the door. Can you answer it? 有人敲門，你去開一下好嗎?
若表示“敲門”，其前既可用搭配介詞at也可用介詞on。如：
Somebody was beating at [on] the door. 有人不停地敲門。
Someone knocked at [on] the door at midnight. 午夜時有人敲門。
They heard a tap at [on] the door. 他們聽見輕輕的敲門聲。
若用介詞in，則需要根據具體語境來確定其含義。如：
The gun shot a hole in the door. 這槍在門上射出一個洞。
She got her fingers caught in the door. 她的手指讓門給夾了。
Directly I walked in the door I smelt smoke. 我一進門，就聞見了煙味。
He stood in the door for several minutes before deciding whether he’d stay. 他站在門里邊好幾鐘才決定是否留下來。
2. by the door與through the door均可指“通過門”，但前者側重方式，后者側重實實在在地“通過”。如：
We couldn’t get the piano through the door. 我們無法將鋼琴搬過這道門。
The thief slipped out by the back door. 那個賊偷偷從后門溜出去了。
漢語說“走后門”，指的是通過不正當的手段來達到某種個人目的，有趣的是，在英語中也有類似用法，用by the back door或through the back door均可。如：
He used his influential friends to help him get into the civil service by the back door. 他利用那些有權有勢的朋友幫助他走后門，到政府行政部門任職。
3. open the door與answer the door均可表示“開門”，但有區別：前者close the door(關門)相對，指把門打開;后者指聽到門鈴響或敲門聲而去開門。如：
He opened the door and went out. 他打開門就出去了。
Will you answer the door? There’s someone knocking. 請你去開門，有人在敲門。
4. show sb the door與show sb to the door只差一個介詞to，但意思區別很大：前者意為指著門要某人出去，即把某人攆走或下逐客令;后者意為送某人到門口，即相當于漢語中的送客。如：
After having insulted his host, he is shown the door. 他侮辱了主人，結果被轟了出去。
Whenever a guest leaves, my father will show him to the door. 每當客人離開時，我父親都把客人送到門口。
show sb to the door 也可說成 see sb to the door。如：(www.yygrammar.com)
Goodbye, Mr Carter. My secretary will see you to the door. 再見，卡特先生，我的秘書將送你到門口。
5. 習語 (from) door to door的本義是“從一家門口到另一家門口”，也就是“逐門逐戶”“挨家挨戶”，相當于 (from) house to house。如：
The journey takes about an hour, door to door. 從這家到那家的路程要用一小時。
We went from door to door collecting money for charity. 我們挨家挨戶地募集慈善捐款。