Answer is: B. beta particles.
Nuclear reaction: ¹⁴C → ¹⁴N + e⁻ + νe (electron antineutrino).
In beta minus decay (atomic number Z is increased by one, from 6 in carbon to 7 in nitrogen) neutron is converted to a proton and an electron and an electron antineutrino.
Beta decay is radioactive decay in which a beta ray and a neutrino are emitted from an atomic nucleus.
