  To lowest-order weak interactions in the standard model, we point out that a
complete graph description of two-body mesonic $B$ (or $D$) decays needs ten
topologically different quark diagrams. The two-body baryonic $B$ decays can be
illustrated in terms of five diagrams. We remark a variety of features of the
graph language. Some pure channels of mesonic $B$ decays, which can be used to
test the quark-diagram scheme, are discussed in some detail.
