采用砂型硬度计测量砂型硬度,手工或一般造型机制造的砂型表面硬度为()单位。
A.40~60
B.60~80
C.80~100
D.100~120
参考答案:B
_____ the ladder, get someone to hold it.
A.When climbed
B.When to climb
C.When climbing
D.When one climbs
孔隙