大部分交易都是私下完成的。

Most of the deals were done ___behind ___closed ___doors.

影响全世界的决定都是私下做出的，并且是最高机密。

Decisions which affect the whole world are made ___behind ___closed ___doors and are top secret.

委员会私下开会讨论这项机密事务。

The committee met ___behind ___closed ___doors to discuss the confidential matter.