Wear a mask ondays when there is heavy pollution.
请帮忙剖析句子。
Wear a mask on days when there is heavy pollution.
when there is heavy pollution 是修饰 days 的定语从句。
句意：污染紧急的日子戴上口罩。
又如：On days when few customers came to shop, I felt overwhelmed by boredom. 店里买卖比较冷清的日子，我感觉无聊极了。