Tired, Jim was fast asleep with his back ____ a big tree.
A.in
B.below
C.beside
D.against
答案:D
应按( )原则进行同种类钢筋代换。
A.钢筋面积不小于代换前
B.钢筋受拉承载力设计值相等
C.钢筋面积相等
D.钢筋强度相等
在矿井条件下,火灾转变为爆炸的条件有哪些?