Definition: air pollution in a city that is a mixture of smoke, gases, and chemicals Level: C1
今天早晨，烟雾笼罩着城市。
The ___smog hung heavily over the city this morning.
需要更严格的排放控制来减少城市地区的烟雾。
Stricter emission controls are needed to reduce ___smog in urban areas.
浓重的烟雾导致呼吸困难，并引发了健康警告。
The thick ___smog made it difficult to breathe and caused health warnings.
