Help me out of this!!!

A functionf is defined on interval (0, 1) as follows when x is irrational f(x)={1 when x is rational no.and lcm(p, q) ==1 q then which one of the following is true? f is continuous at each irrational point and discontinuous at each rational point f is continuous at each rational point and discontinuous at each irrational point A) (B) f is discontinuous at each rational and irrational points (C) (D) f is continuous at each rational and irrational points