The function f(x)={4π+tan−1x,21(∣x∣−1),∣x∣≤1∣x∣>1 is
(a) both continuous and differentiable on R−{−1}
(b) both continuous and differentiable on R−{1}
(c) continuous on R−{−1} and differentiable on R−{−1,1}
(d) continuous on R−{1} and differentiable on R−{−1,1}