V型缺口冲击试样的底部曲率半径是（）mm。
A.0.25
B.0.20
C.0.30
参考答案：A
In the cafeteria, I saw my sister and her three friends, none of ____ I had ever seen before.
A．them
B．which
C．whom
D．those
3a（a2-2a+1）-2a2（a-3）=______．
