Wear a mask on days when there is heavy pollution.
请帮忙分析句子。
when there is heavy pollution 是修饰 days 的定语从句。
句意:污染严重的日子戴上口罩。
又如:On days when few customers came to shop, I felt overwhelmed by boredom. 店里生意比较冷清的日子,我感觉无聊极了。