keep one's voice down

例句：

1. 1. The team needs to keep the temperature at a comfortable level.
   团队需要将温度保持在舒适的水平。
2. 2. We need to keep an eye on the children while they are playing outside.
   我们需要在孩子们在外面玩耍时留意他们。
3. 3. The economy is expected to keep growing in the coming years.
   预计经济在未来几年将继续增长。