体积安定性是指水泥净浆硬化后的体积变形的均匀适度性,当水泥中掺入过量的()时会造成水泥的体积安定性不良
A.石灰石
B.石膏
C.红土
D.矿碴
参考答案:B
The parents were unsettled for the first few days, _____ about their son's safety. [ ]
A. having worried
B. to worry
C. being worried
D. worried
万一发生火灾,导游员应( )。
A.立即报警
B.带大家搭乘电梯
C.迅速通知领队及全团旅游者
D.配合工作人员,听从统一指挥,迅速通过安全出口疏散旅游者
E.引导大家自救