Tetragonal crystal system has the following unit cell dimensions (a) a = b = c and α = β = γ = 90∘ (b) a = b ≠ c and α = β = γ = 90∘ (c) a ≠ b ≠ c and α = β = γ = 90∘ (d) a = b ≠ c and α = β = 90∘