Self-consistent light-front quark model analysis of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>B</mml:mi><mml:mo stretchy="false">?</mml:mo><mml:mi>D</mml:mi><mml:mo>?</mml:mo><mml:msub><mml:mrow><mml:mi>?</mml:mi></mml:mrow><mml:mrow><mml:mo>?</mml:mo></mml:mrow></mml:msub></mml:mrow></mml:math> transition form factors

We investigate the transition form factors $f_+(q^2)$ and $f_-(q^2)$ [or $f_0(q^2)$] for exclusive semileptonic $B\to D\ell\nu_\ell$ $(\ell=e, \mu,\tau)$ decays in standard light-front quark model (LFQM) based on LF quantization. The common belief is that while can be obtained without involving any treacherous contributions such as zero mode instantaneous contribution, receives those since it involves at least two components of current, e.g. $(J^+, J^-)$ or {\bf J}_\perp)$. Contrary to belief, we show Drell-Yan ($q^+=0$) frame from gives identical result J}_\perp)$ LFQM. In our numerical calculations, obtain branching ratios compare with experimental data well other theoretical predictions. Our results ${\rm Br}(B\to D\ell\nu_\ell)$ reasonable agreement except semitauonic $B^0\to D^-\tau\nu_\tau$ decay. ratio ${\cal R}(D)=\frac{{\rm D\tau\nu_\tau)}{{\rm D\ell'\nu_{\ell'})}$ $(\ell'=e,\mu)$ also estimated compared