在电化区段通过铁路平交道口的汽车、拖拉机等运输工具装载货物高度超过（）以上严禁坐人。
A、4.2m
B、2
C、3
D、2.5
参考答案：B
中周期的平均长度为（）。
A．8～10年
B．50年
C．10～15年
D．5～8年
A painter has painted one-third of a rectangular wall which is ten feet high. When she has painted another 75 square feet of wall, she will be three-quarters finished with the job. What is the length (the horizontal dimension) of the wall
A．18 feet
B．12 feet
C．10 feet
D．9 feet
E．(E) 6 feet
