Consider two cylindrical conductors A and B, made of the same metal connected in series to a battery. The length and the radius of B are twice that of A. If $\mu_{\text{A}}$ and $\mu_{\text{B}}$ are the mobility of electrons in A and B respectively, then $\frac{\mu_{\text{A}}}{\mu_{\text{B}}}$ is : (A) $\frac{1}{2}$ (B) $\frac{1}{4}$ (C) $2$ (D) $1$