A plot of speed-density relationship (linear) of two roads (Road $\mathrm{A}$ and Road $\mathrm{B}$) is shown in the figure.
If the capacity of Road $\mathrm{A}$ is $C_A$ and the capacity of Road $\mathrm{B}$ is $C_B$, what is $\frac{C_A}{C_B}$?
- $\frac{k_A}{k_B}$
- $\frac{u_A}{u_B}$
- $\frac{k_A u_A}{k_B u_B}$
- $\frac{k_A u_B}{k_B u_A}$