behind closed doors

1. 秘密的（地）
   It was a bitter debate behind closed doors.

   那是场秘密的激烈辩论。

by the back door

1. 走后门；不合法地
   They did it by the back door.

   他们靠走后门干的。

from door to door

1. 挨家挨户地
   She sells cosmetics from door to door.

   她挨家挨户地推销化妆品。

next door to

1. 与……相邻
   They lived next door to each other.

   他们的住所相邻。

2. 几乎
   It was next door to impossible.

   那简直不可能。

open the door(s) to

1. 为……开门；为……提供机会
   The policy has opened the doors to advances in technology.

   这项政策已为技术发展开了大门。

out of doors

1. 在露天；在户外
   It's cold out of doors.

   外面很冷。

slam the door in sb.'s face

1. 把某人拒之门外
   When George came to his boss for help, the latter slammed the door in his face.

   当乔治找他老板帮忙时，老板把他拒之门外。

• lay something at someone's door
  blame someone for something.
• out of doors
  in or into the open air.