The fact that form factors do not depend on the choice of wave function can also be seen by comparing our result with the one given in the first row of the table \[tab1\], which came from using the wave function (\[wf3\]).

The E653 Collaboration determined the following ratio of decay rates [@E653]: $$\begin{aligned}
 \frac{\Gamma  (D^{+}\rightarrow \rho^{0}
\mu^{+} \nu )} {\Gamma (D^{+}\rightarrow  \bar{K^{*}}^{0} \mu^{+}
\nu )} & = &  0.044  ^{+0.031}_{\! \, -0.025} \pm 0.014 \label{eq:E653} \end{aligned}$$

Using this and the values given in the last row of the Table for the form factors of $D\rightarrow  \rho  $ and $D\rightarrow
K^{*}$, we can extract the following result on the ratio of the CKM matrix elements $|V_{cd}/V_{cs}|$: $$\begin{aligned}
|V_{cd}|/|V_{cs}|  & = &  0.214  ^{+0.074}_{  \!  \,  -0.060} \; .  
\label{eq:OT3}\end{aligned}$$ which is consistent with, but not as accurate as, the prediction derived from the values quoted in PDG [@PDG], coming from the unitarity constraint: $$\begin{aligned}
|V_{cd}|/|V_{cs}|  & = & 0.226  \pm  0.003 \; .  \label{eq:OT3.a}\end{aligned}$$

Lepton Mass Effects
-------------------

Most of the theoretical and experimental analyses of the exclusive semileptonic decays assume that taking the lepton mass to be zero is a good approximation. For the electron and $\tau$–lepton cases, the 