Copper wire comes in set lengths but with a range of diameters $d$. Each wire has its own resistance $R$. Which relationship between $R$ and $d$ is correct?
- A$R$ is directly proportional to $d$.
- B$R$ is directly proportional to $d^{2}$.
- C$R$ is inversely proportional to $d$.
- D$R$ is inversely proportional to $d^{2}$.