A significant fraction of the radiation dose you will receive during your life comes from radioactive materials in your body. The most important source of this radiation is the potassium isotope ⁴⁰K, which decays to the stable calcium isotope ⁴⁰Ca. What particle is emitted in the decay? 

A. A helium nucleus  

B. A neutron 

C. An electron

D. A positron