下列建筑材料，哪一类的抗震性能最好()
A．砖石材料
B．木材
C．钢材
D．钢筋混凝土
参考答案：B
I'm __________ tired, because I have __________ homework.[ ]
A. too much, too many
B. much too, too much
C. much too, too many
D. too many, too much
主要承受轴向载荷的滚动轴承称为（）。
A.向心轴承
B.推力轴
C.向心推力轴承
D.滑动轴承
