If one knows little about particle physics, one can make (at least) the following deductions, wherein one recalls the composites of each particle:

(A) A muon is a lepton. Leptons, along with quarks, are considered the fundamental particles.

(B) Pi-Meson consists of a quark and its antiparticle. (Contribution to this part of the solution is due to user danty.) Moreover, a pi-meson is a hadron. Hadrons interact with the strong-force, and all of them are composed of combinations of quarks. (The fundamental particles are classified as quarks and leptons.)

(C) A neutron is made up of 3 quarks.

(D) A deuteron consists of a proton and a neutron. (tritium is two neutrons and a proton, while regular Hydrogen is just an electron and proton)

(E) An alpha particle consists of electrons and protons and neutrons.


Choice (A) remains. Choose that.

If one has some time, one might want to remember the elementary particles involved in the Standard Model. There are six quarks and six leptons. Three of the leptons are neutrinos and the other three are the electron, the tau, and the muon. (Also, in a decay similar to beta-decay, a muon is emitted instead of an electron. Charge conservation works since a muon is like an electron except it is about 200 times more massive.)

Wikipedia has a good reference on this:
\begin{verbatim} http://en.wikipedia.org/wiki/Fundamental_particle
\end{verbatim}