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)=______.