钥匙在门上用in。in虽然也翻译为在门上，但钥匙是插在门里面，所以用in。例如，The key is in the door。
in the door例句
They put the key in the door and entered.
他们用钥匙打开门进去了。
I looked everywhere for my keys and they were in the door all the time.
我到处找钥匙，没想到钥匙一直插在门上。
The key turned in the door, and I could hear the feet of the guards outside.
钥匙插在锁孔里，我可以听到外面卫兵的脚步声。
on the door例句
They had put a padlock on the door of his flat.
他们已经在他的公寓门上上了把挂锁。
There was an old rusting bolt on the door.
门上有一个生锈的旧门闩。
The lock on the door is rusty and won't open.
门上的锁锈住了。
