影响水泥安定性的主要化合物（）。
A.石膏、游离MgO
B.游离CaO、三氧化硫
C.游离Ca0、游离MgO
D.石膏、三氧化硫
参考答案：C
A．(A) He asks the porter to carry his suitcase to his room.
B．(B) He wants a morning call at 7 o’clock the next day.
C．(C) He thinks the woman at the reception is very helpful.
D．(D) He puts the woman’s pen in his pocket by mistake.
某分部工程双代号网络计划如右图所示，下列对其作图错误表述不正确的是（）。
A．有多个起点节点
B．有多个终点节点
C．节点编号有误
D．有多余虚工作
