电脑风扇在安静地嗡嗡作响。

The computer fan is ___humming quietly.

她一边整理书架一边轻声哼着歌。

She was ___humming softly while organizing the bookshelf.

市场里人群熙熙攘攘，热闹非凡。

The marketplace was ___humming with shoppers and vendors.