对强度等级C60的高强混凝土,其粗骨料的最大颗粒要求( )。
A.不应大于25 mm B.不应大于31.5 mmC.不应小于25 mm D.不应小于31.5 mm
参考答案:B
在输气管道内壁建立一层内壁涂层,不仅可以防腐,而且可以提高输气
— Tom is never late for work. Why is he absent today?
— Something _____ to him. [ ]
A. must happen
B. should have happened
C. could have happened
D. must have happened