题干
Many students write to the Language Doctor to______ advice about learning English.
A：look through
B：ask for
C：give up
D：worry about
答案(点此获取答案解析）
B
2SO3，如果SO2的起始浓度为2 mol/L ，2min后SO2的浓度为1.8mol/L，则用SO2的浓度变化表示的反应速率为（ ）