necessity的形容詞形式是什么

　　This is a necessary consequence of progress.

　　這是發展的必然后果。

　　Repairs are necessary to strengthen the bridge.

　　這座橋需要加固。

　　A radical overhaul of the tax system is necessary.

　　有必要徹底改革稅制。

　　For him, reading was a necessary prelude to sleep.

　　對他來說，閱讀是入睡的必要前奏。

　　The alliance stands ready to do what is necessary.

　　該聯盟已準備好采取必要行動。