A:CO2
B:SO2
C:可吸入颗粒物
D:NO2
—Which is more useful, reading or writing?
—I think _______ of them are useful.
已知集合A=x|x>1,B=x|x2-2x<0,则A∪B=( )
①人 ②阳光 ③蚜虫 ④空气 ⑤田鼠 ⑥水 ⑦蚯蚓 ⑧土壤.