毛石砌筑时必须设置拉结石，应均匀分布，一般每间隔1m至少设置（）。
A.一块
B.二块
C.三块
D.由墙体强度来定
参考答案：A
—I think I will recommend David as the chairperson of the club because he is .
—I quite agree with you. He is always willing to share his things with others.
A．practical
B．active
C．generous
D．energetic
分析USB单端反激式充电器控制电路原理。
