Two spherical conductors A and B of radii o and b (b > a) are placed con-centrically in air. The two are connected by a copper wire as shown in fig. Then the equivalent capacitance of the system is

• A

  $\frac{4{\mathrm{\pi \epsilon }}_0\mathrm{ab}}{\mathrm{b}-\mathrm{a}}$

• B

  $4{\mathrm{\pi \epsilon }}_0(\mathrm{a}+\mathrm{b})$

• C

  $4{\mathrm{\pi \epsilon }}_0\mathrm{b}$

• D

  $4{\mathrm{\pi \epsilon }}_0\mathrm{a}$