Which of the following is true: A. If a cos A = b cos B, then the triangle is isosceles or right angled. B. If in a triangle ABC, cos A cos B + sin A sin B sin C =1 then the triangle is isosceles right angled. C. If the ex-radii r1, r2, r3 of ΔABC are in the HP, then it's sides are not in AP Choose the correct answer from the options given below :