Paul is very proud ______ his father because he helps keep our city beautiful. [ ]

A. in

B. of

C. on

D. from

在下述条件中，较易形成带状切屑的是（）。

A.切削塑性材料时

B.切削脆性材料时

C.较小的切削厚度

D.刀具前角较小时

E.较高的切削速度