  The decay $B\to f_0(980)K is studied within the framework of QCD
factorization and the two-quark scenario for $f_0(980)$. There are two distinct
penguin contributions and their interference depends on the unknown mixing
angle $\theta$ of strange and nonstrange quark contents of $f_0(980)$:
destructive for $0<\theta<\pi/2$ and constructive for $\pi/2<\theta<\pi$. The
QCD sum rule method is applied to evaluate the leading-twist light-cone
distribution amplitudes and the scalar decay constant of $f_0$. We conclude
that the short-distance approach is not adequate to explain the observed large
rates of $f_0K^-$ and $f_0\ov K^0$. Among many possible subleading corrections,
we study and estimate the contributions from the three-parton Fock states of
the $f_0$ and from the intrinsic gluon inside the $B$ meson. It is found that
the spectator gluon of the $B$ meson may play an eminent role for the
enhancement of $f_0(980)K$. We point out that if $f_0(980)$ is a four-quark
state as widely perceived, there will exist extra diagrams contributing to
$B\to f_0(980)K$. However, in practice it is difficult to make quantitative
predictions based on the four-quark picture for $f_0(980)$ as it involves
additional nonfactorizable contributions that are difficult to estimate and the
calculations of the decay constant and form factors of $f_0(980)$ are beyond
the conventional quark model.
