  Two body decays of charm mesons are studied by describing their amplitude in
terms of a sum of factorizable and non-factorizable ones. The former is
estimated by using a naive factorization while the latter is calculated by
using a hard pseudo-scalar-meson approximation. The hard pseudo-scalar-meson
amplitude is given by a sum of the so-called equal-time commutator term and
surface term which contains all possible pole contributions of various mesons,
not only the ordinary $\{q\bar q\}$ but also four-quark $\{qq\bar q\bar q\}$,
hybrid $\{q\bar qg\}$ and glue-balls.
  Naively factorized amplitudes for the spectator decays which lead to too big
rates can interfere destructively with exotic meson pole amplitudes and the
total amplitudes can reproduce their observed rates. The non-factorizable
contributions can supply sufficiently large contributions to the color
suppressed decays which are strongly suppressed in the naive factorization. A
possible solution to the long standing puzzle that the ratio of decay rates for
$D^0\to K^+K^-$ to $D^0\to \pi^+\pi^-$ is around 2.5 is given by different
contributions of exotic meson poles.
