轧辊按制造材料分可分为()、()、()。
参考答案:铸钢系列轧辊、铸铁系列轧辊、锻造系列轧辊
能够模式化为维属性和度量属性的数据统称为()数据。
My e-mail ______ to you last night. Have you received it ______ ? [ ]
A. sent; yet
B. is sent; already
C. was sent; yet