results obtained using $A_{1}$ and $A_{2}$ are so large that they obscure the real value of $A_{0}$. For the non–zero lepton mass case, use of $A_{1}$, $A_{2}$ and $V$ does not connect smoothly to the zero lepton mass results. When $A_{2}$ is used in place of $A_{1}$ the $SU(3)$ symmetry breaking remains small for a range of $q^2$, even though there is a more complicated collection of form factors.

It is interesting to note the predictions of [@BFO] obtained in a framework based on HQET and chiral symmetries. Although their values for the form factors for $D\rightarrow  \rho $ and $D\rightarrow  K^{*} $ agree with the predictions of other models given in the table, the result of $B\rightarrow  \rho$ is larger than most of the others.

It is claimed sometimes that the light-front quark model is ruled out since it typically gives a value about $15\%$ less than one for the ratio $R=f^{D\rightarrow   \pi}_{+}(0)/f^{D\rightarrow
K}_{+}(0)$. The experimental value of $R$ is obtained from the measurements of the decays $D^{0}\rightarrow K^{-} e^{+} \nu_{e}$ and $D^{+}\rightarrow   \pi^{0}  e^{+}  \nu_{e}$ by MARK–III [@MARK] and CLEO–II [@CLEO]:

$$\begin{aligned}
\frac{Br(D^{+}\rightarrow \pi^{0} e^{+} \nu_{e})}{Br(D^{0}\rightarrow 
K^{-} e^{+} \nu_{e})} & = & \left\{ \begin{array}{lll} 
(8.5 \pm 2.7 \pm 