硅酸盐水泥石在温度为250°C 时,水化物开始脱水,水泥石强度下降,因此硅酸盐水泥不宜单独用于( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
免费的网站请分享给朋友吧