noise的形容詞的反義詞是？

　　例句：

　　The engine is very noisy at high speed.

　　這個發動機轉速高時噪音非常大。

　　Our next-door neighbours are very noisy.

　　我們隔壁的鄰居非常吵。

　　This area can be very noisy at night-time.

　　這個地方夜間有時會非常吵。

　　When I approached, they grew silent.

　　當我走近時，他們變得沉默了。

　　She was silent, smiling mysteriously.

　　她沉默不語，神秘地笑著。

　　Her voice quavered and she fell silent.

　　她的聲音顫抖著，繼而沉默了下來。