網友回答：
it is a serious threat to us because.it means the poisoning of the air， rivers and lands，there are many factories that bring pollution to us. we can not have fresh air in the morning. this is mainly because of the poisonous smoke coming from factories，相反
溫馨提醒：隨時光變遷，文中所陳述觀點；準確性、難免有所變動，因此文中觀點僅供參考。
