D mesons are the lightest mesons that contain a charm quark or anti-quark. (a) Explain why D mesons can only decay via weak interactions. (b) Draw Feynman diagrams for the decays D K-++ and D K+K+, where the quark contents are as follows: D is cu, K- is su, and K+ is us. (c) Show that the ratio of the decay rates Ipo K-++ Ipo+K+K+ is approximately 100:1. You may use the value 0c = 13.1 for the Cabibbo angle, and the meson masses mpo = 1865 MeV, mk = 494 MeV, and m+ = 140 MeV.