Do you have ________QQ number? [ ]
A. a
B. an
C. the
D. /
答案：A
Our teacher ______ to Beijing many times . He knows Beijing very well.[ ]
A. goes
B. is going
C. has gone
D. has been
微库仑滴定法中硫化物主要是转化成（）。
A.二氧化硫
B.二氧化碳
C.三氧化硫
D.硫酸
