如果天气很冷，我们会说"It's cold. Put on a jacket."这个短语来提醒人们加衣服。这个短语来源于英语中常用的日常对话，用来提醒人们注意自己的身体和保暖。例句如下：
It's cold outside. Put on a jacket before you go out.
The weather forecast says it's going to be cold tonight. You should put on a jacket.
Don't forget to put on a jacket. It's cold in here.
在上面的例句中，"put on a jacket"是一个祈使句，用来给人们提醒加衣服。