构成不确定度的来源包括的方面有：所用的参考标准和标准物质、方法和设备、环境条件、被检测或校准物品的性能和状态以及操作人员等等。
参考答案：对
表面淬火的零件常用低碳结构钢制造，经表面淬火后获得高硬度。
It's two years since they ____ each other, and they are going to get married next month. [ ]
A. were in love with
B. fell into love with
C. have loved
D. fell in love with
