The quark compositions of the proton and neutron are, respectively, uud and udd, where \(\mathrm{u}\) is an up quark (charge \(+\frac{2}{3} e\) ) and \(\mathrm{d}\) is a down quark (charge \(-\frac{1}{3} e\) ). There are also antiup \(\overline{\mathrm{u}}\) (charge \(-\frac{2}{3} e\) ) and antidown \(\overline{\mathrm{d}}\) (charge \(+\frac{1}{3} e\) ) quarks. The combination of a quark and an antiquark is called a meson. The mesons known as pions have the composition \(\pi^{+}=\mathrm{u} \bar{d}\) and \(\pi^{-}=\overline{\mathrm{u}} d\). Suppose a proton collides with an antineutron. During such collisions, the various quarks and antiquarks annihilate whenever possible. When the remaining quarks combine to form a single particle, it is a A. Proton B. Neutron C. \(\pi^{+}\)

D. \(\pi^{-}\)