U型钢拱形支架采用U型钢制造，具有可缩性，多用于地压大，受采动影响显著的采区巷道。
参考答案：对
不属于人口容量特点的是[ ]
A、临界性
B、相对性
C、警戒性
D、均衡性
Fair and(1) competition in government procurement around the world is good business and good public policy. Competitive pricing, product(2)and performanceimprovements result from competitive practices and help ensure that government authoritiesget the best (3)for the public they serve.
空白（3）处填（）
A.help
B.server
C.value
D.policy
