The president underscored the need for (A) a constructive and a realistic dialogue (B) of issues of global interest.(C)

My book says part (B) of sentence is wrong, we don't need to use a here, I agree with that but isn't part (C) also wrong ? I guess it should be dialogue ON issues of global interest. Am I correct ?

Edit : by a I am referring to second a, the one which is with realistic.