某厂生产的2000件产品中,有不合格产品m件,今分10次各抽取50件产品进行检测,平均有不合格产品1件,对m的叙述正确的是 ( )
A:m=40
B:m≠40
C:m的值应在40左右
D:无法确定
若tanα=﹣2,α是直线y=kx+b的倾斜角,则α=____ .(用α的反正切表示)
—It's so late. Why not write the report tomorrow?—But I don't know _______ I can do it if not now.
It's necessary for these children to____ ____ ____ .