Which team ____ you ____ (support) for the basketball match tomorrow night?
-----I'm waiting for the mail. Do you know it will arrive?
-----Usually it comes by 4:00 p.m.
下列化学符号①NO2 ②2NO ③SO42﹣ ④MgO+2中,数字“2”表示元素化合价数值的是(填序号,下同) ____;表示分子个数的是 ____; 表示每个分子中所含某元素原子个数的是 ____;表示一个离子所带的电荷数值的是 ____