我在大楼门口跟保安打招呼。

I greet the ___security ___guard at the building entrance.

他是一个孤寂的守卫者。

He is a lonely ___guard.

保安在银行门口守卫着。

The security ___guard the entrance of the bank.

这个机器需要一个金属防护罩来保护操作员。

This machine requires a metal ___guard to protect the operator.

拳击手在比赛中始终保持着防守姿势。

The boxer always keeps his ___guard up during the match.