For a real number x let [x] denote the largest number less than or equal to x. For x ∈ R let f (x) = [x] sin πx. Then
(A) f is differentiable on R.
(B) f is symmetric about the line x = 0.
(C) ∫ f(x) ∈[3,-3] dx = 0
(D) For each real α, the equation f (x) – α = 0 has infinitely many roots