混凝土的抗冻性是指混凝土在饱和状态下,经多次冻融循环作用而不严重降低强度的性能,其抗压强度下降不超过25%,质量损失不超过()。
A.3%
B.5%
C.7%
D.9%
参考答案:B
---Must we leave the classroom now?
---No, you _____. You _____ leave after the bell rings.
A.mustn't; are allowed to
B.don't have to; might
C.needn't; can
D.can't; are supposed to
拥有近1.8亿亩耕地的黑龙江省,素有“中国粮仓”的美誉,黑龙江的地表结构特征可概括为[ ]
A.三山夹两盆
B.山环水绕,平原居中
C.中间高,四周低
D.地表平坦