Quadrilateral ABCD is inscribed in circle P as shown. Which statement is necessarily true? A. m∠A + m∠B = m∠C + m∠D B. m∠A + m∠C = m∠B + m∠D C. m∠A + m∠D = m∠B + m∠C D. m∠A + m∠B = 2(m∠C + m∠D)