空调发出低沉的嗡嗡声。

The air conditioner is ___humming quietly.

他在等公交时轻轻哼着一首老歌。

He was ___humming an old song while waiting for the bus.

周末的市场人声鼎沸，讨价还价声和欢笑声此起彼伏。

The weekend market ___hums with the sound of bargaining and laughter.