设防地段的隧道宜采用带仰供的曲墙式衬砌。其中Ⅳ－Ⅵ级围岩地段宜采用（）。
参考答案：钢筋混泥土
It was after he got what he had wanted very much _______ he realized it was not important.
A．when
B．that
C．since
D．as
专为升降人员或物料用的钢丝绳，当一个捻距内断丝面和同钢丝绳总面积之比达到百分之多少时必须更换？
