这艘潜艇服役20年后被正式退役了。

The submarine was officially ___decommissioned after 20 years of service.

由于老化严重，这座核电站已被正式停用。

The nuclear power plant was officially ___decommissioned due to severe aging.

这艘军舰服役30年后正式退役了。

The warship was officially ___decommissioned after 30 years of service.