  According to the heavy-quark flavour symmetry, the $B\to \pi, K$ transition
form factors could be related to the corresponding ones of D-meson decays near
the zero recoil point. With the recent precisely measured exclusive
semileptonic decays $D \to \pi \ell \nu$ and $D\to K \ell \nu$, we perform a
phenomenological study of $B \to \pi, K$ transition form factors based on this
symmetry. Using BK, BZ and Series Expansion parameterizations of the form
factor slope, we extrapolate $B \to \pi, K$ transition form factors from
$q^{2}_{max}$ to $q^{2}=0$. It is found that, although being consistent with
each other within error bars, the central values of our results for $B \to \pi,
K$ form factors at $q^2=0$, $f_+^{B\to \pi, K}(0)$, are much smaller than
predictions of the QCD light-cone sum rules, but are in good agreements with
the ones extracted from hadronic B-meson decays within the SCET framework.
Moreover, smaller form factors are also favored by the QCD factorization
approach for hadronic B-meson decays.
