地下室的天花板上有一个活板门可以通往阁楼。

There is a ___trapdoor in the basement ceiling leading to the attic.

城堡的地下室有一个隐蔽的活板门，通向城墙外的逃生路线。

There was a hidden ___trapdoor in the castle's basement leading to an escape route outside the city walls.

程序员在代码中发现了一个可能危及安全的后门。

The programmer discovered a ___trapdoor in the code that could compromise security.