lighten up 用法？

lighten up 放轻松；开心一些；别那么严肃

If someone tells you to lighten up, they think you should be less serious and make an effort to be more relaxed and happy.

light up

1.照亮；发亮

2.现出吃惊的神情；露出喜色

3.点烟；开始吸烟

你的第一个句子错了吧

网上有个四岁姐姐开导2岁弟弟的视频是

You need to toughen up a bit .你要坚强一点。