单阀制动时，制动缸的压力最高不超过（）。
A.350kPa
B.300kPa
C.240~260kPa
D.450kPa
参考答案：B
- Do you have any plan this summer vacation, Mary?
- Sure, I’ d like to be a volunteer and help to _________ the Central Park. [ ]
A. put up
B. call up
C. clean up
D. cheer up
对于采用原木下弦的木桁架，其跨度不宜大于( )项数值。
A．12m B．15m C．18m D．21m
