Consider two concentric spherical surfaces `S_1` with radius a and `S_2` with radius 2a, both centered at the origin. There is a charge +q at the origin and there are no other charges. Compare the flux `phi_1` through `S_1` with the flux `phi_2` through `S_2`.
A. `phi_1 = 4phi_2`
B. `phi_1 = 2phi_2`
C. `phi_1 = phi_2`
D. `phi_1 = phi_2//2`