When Radium-226 Is Transmutated by a Nuclear Decay to Radon-222 $\alpha$

When radium-226 is transmutated by a nuclear decay to radon-222, the process involved is

A) emission of $\alpha$ -particle.
B) emission of $\beta$ -particle.
C) emission of a $\gamma$ -ray.
D) emission of a positron.
E) capture of an electron.