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) `