Two wires A and B are made of same material and have the same length but different cross-sectional areas. If the resistance of wire A is 9 times the resistance of wire B, the ratio of the radius of wire A to that of wire B is:
1
9 ∶ 1
2
1 ∶ 3
3
1 ∶ 9
4
More than one of the above
5
None of the above