Number of points where |f(x)| is not differentiable is (A) 1 (B) 2 (C) 3

Question

Let a function is defined as 

where [ . ] denotes greatest integer function.

Number of points where |f(x)| is not differentiable is 

(A) 1 

(B) 2 

(C) 3 

(D) 4

Answer 1

Answer is (C) 3

At -1, -1/2, 1/2 the function is not differentiable (see Fig.).