Well,
A. I know that alpha decay is the process of expelling a helium atom, or two protons and two neutrons. Those are particles.
B. Beta decay releases either a proton or an electron. Those are also particles.
C. Gamma decay releases a gamma ray, or high-energy photon. A photon is a particle.
D. I don't know much about electron decay, but since it is the only one left, I would go with this one by reason of deduction.
