套管是工艺管道安装中的常用部件,其中,()套管只适用于穿过一般建筑物楼层或墙壁不需要密封的管道。
A.柔性
B.刚性
C.钢管
D.铁皮
参考答案:C, D
定义在[-5,5]上的单调递减的奇函数f(x)满足f(a+1)+f(1-2a)>0,求实数a的取值范围.
They would not allow him _____ across the enemy line. [ ]
A. to risk going
B. risking to go
C. for risk to go
D. risk going