how long you didn't see a blue sky with some white clouds?

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frankly, i can't see pure blue sky in my city, because the air pollution here is very seriously, so i haven't see blue sky and stars for over 4 years. my hometown is a pure city, although there are some factories in it. the sky is blue, and the cloud is white, and the air is fresh. i feel i was reborn. i miss those natural scenes very much. so please cherish the environment in your city.