对于压力大于6MPa的室外燃气管道不允许采用的管材是（）。
A.A级钢管
B.B级钢管
C.球墨铸铁管
D.聚乙烯管
参考答案：B, C, D
A．CPU
B．memory
C．resources
D．information
Can you tell me how much a radio like this costs?（）
A.I‘d like to buy it.
B.It‘s of very good quality.
C.About eighty-five dollars.
D.It depends on how you like it
