the decay rates given by the E653 collaboration we show that the determination of the ratio of the CKM matrix elements is consistent with that obtained from the unitarity constraint. At present, though, the unitarity method still has greater accuracy. For $B$ decays, the decay $B \rightarrow  K^{*} \ell  \bar{\ell}$ at $q^2=0$ involves an extra form factor coming from the photon contribution and so is not amenable to the same kind of analysis, leaving only the decay $B \rightarrow  K^{*} \nu  \bar{\nu}$ as a possibility. This is not an easy mode to determine experimentally.

The results obtained in our model for the form factor $A_{0}(0)$, for $D$ decays, as well as other models are collected in table \[tab1\]. We see that theoretical predictions of the ratio of form-factors fall in a range near $1$. If $A_{0}(0)$ is obtained from Eq. (\[def\]) with the calculated values of $A_{1}$ and $A_{2}$ then there may be difficulties coming from the $q^{2}$ dependences of the form factors and also from possible correlations in treating the errors. The comparison with QCD sum rules predictions [@Ball] ,[@Nar],[@Slob] shows a similar problem (the exception is ref. [@CFS], where $A_{0}$ is directly calculated ): the uncertainities in the 