焦炭灰份中的主要化学成份是MgO和CaO。（）
参考答案：错
— ______do you go to the park?
—Three times a month. [ ]
A. How long
B. How often
C. How much
D. How far
A．mgtgθ
B．mgsinθ
C．μmg
D．μmg
mgtgθ
mgsinθ