For reasons of security the door is always kept locked.

　　為了保證安全，門總是鎖著的。

　　The agreement will open the door to increased international trade.

　　此協議將會提供增加國際貿易的機會。

　　The government's policy is an open door to disaster.

　　政府的政策為災難敞開了大門。

　　There's building work going on next door.

　　鄰居正大興土木。