简述压印缺陷特征。
参考答案：薄带钢表面呈现一定深度的凹坑，有周期性，多少不一，缺陷处颜色较亮。
Students have turned to _____ English hard because the new English teacher keeps _____ them to learn it. [ ]
A. study; to encourage
B. studying; encouraging
C. study; on encouraging
D. studying; to encourage
生育酚中生物活性最大的是（）
A.α-生育酚
B.β-生育酚
C.γ-生育酚
D.δ-生育酚
E.三烯生育酚
