下列（）项对结构的作用不属于可变荷载的范畴。
A.楼面活荷载
B.风荷载
C.雪荷载
D.撞击力或爆炸力
参考答案：D
So much of interest that most visitors simply run out of time before seeing it all. [ ]
A. offers Beijing
B. Beijing offers
C. does Beijing offer
D. Beijing does offer
盈亏平衡点是根据（）三者之间相互制约关系的综合分析。
A.产量
B.业务量
C.成本
D.利润
