Final State Interactions, Resonances and CP Violation in D and B Exclusive Decays

Hadron resonances affect nonexotic $D^o$ decays but not $B$ decays which are far from the resonance region. We obtain new information from {\bf exclusive} decays and show that interference between colour favoured and colour suppressed diagrams is {\bf constructive} in $B$ and (some) $D$ decays in contrast to the inclusive decays where a net Pauli destructive interference is claimed. We suggest that a systematic study of $B$ decay final states containing excited mesons such as $a_1 D$ or $\pi D^{**}$ show opposite behaviour for $B^o$ and $B^+$ relative to the ground state channels. We give inequalities among final state branching ratios for several $B$ and $D$ channels. Decays into $\pi K^{(*)}$ and $\rho K^{(*)}$ appear to show different behaviours.