Three concentric metal shells A, B and C of respective radii a, b and c (a < b < c) have surface charge densities +σ, –σ and +σ respectively. The potential of shell B is :-

a) σ/ε₀ [{(b²-c²)/b} + a]
b) σ/ε₀ [{(b²-c²)/c} + a]
c) σ/ε₀ [{(a²-b²)/a} + c]
d) σ/ε₀ [{(a²-b²)/b} + c]