进行水泥试验筛标定时，应使用水泥细度标准样品。每个试验筛的标定应取2个标准样品连续进行，中间不得插做其它样品试验。
参考答案：对
若|x-y+1|+（y+5）2=0，则xy=______．
---Hi, Tom. Any idea where Jane is?
---She in the classroom. I saw her there just now.
A．shall be
B．should have been
C．must be
D．might have been
