有永久性顶盖的室外楼梯，应按建筑物自然层的( )面积的1/2计算。
A．六面
B．四面
C．水平投影
D．三面
参考答案：C
As soon as I shut the front door, I realized that I ______ my key in the house. [ ]
A. had left
B. had forgotten
C. had put
D. had placed
室内燃气管道沿墙安装，与其他管道相遇时，净距不宜小于150mm的有()。
A.与水平平行敷设的给水管
B.与竖向平行敷设的热水管
C.与交叉敷设的给水管
D.与交叉敷设的热水管
