  The two-body mesonic $B$ decays induced only via a single $W$-exchange or
annihilation quark diagram, such as $B^-_u\rightarrow D^{(*)-}_sK^{(*)0}$ and
$\bar{B}^0_d\rightarrow D^{(*)+}_sK^{(*)-}$, are analyzed in the factorization
approximation. We estimate the branching ratios for those transitions into two
pseudoscalar mesons, and find them to be negligibly small. The significant
effect of final-state rescattering is illustrated by taking $B^-_u\rightarrow
D^-\bar{K}^0$ for example.
