Every person stood to applaud his unforgettable act of courage.

　　所有人起立為他不可磨滅的英勇之舉鼓掌。

　　My first love was unforgettable.

　　我的初戀難以忘懷。

　　A visit to Rome will be unforgettable.

　　到羅馬一游將會令人永遠難忘。

　　He created many unforgettable characters in his novels.

　　他在他的小說中創造了很多令人難忘的人物。

　　He spent so many unforgettable days with them that he was loath to part with them.

　　他與他們一起度過那么多難忘的日子，他舍不得離開他們。