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，神祕地笑着。

Her voice quavered and she fell silent.

她的聲音顫抖着，繼而沉默了下來。