hum bar

例句：

1. 1.The bee hums a sweet melody in the morning.
   蜜蜂在早上发出甜美的旋律。
2. 2. The hum of traffic is constant in this area.
   这个地区的交通噪音持续不断。
3. 3.She hummed a tune to herself as she walked home.
   她边走边哼唱着小调回家。