The Venn diagram shown below compares the nuclear reactions in the sun and nuclear power plants. Picture shows two ovals which overlap in the middle. The oval on the left has the label 'Sun' on top and 'Combining of atoms' within it. The oval on the right has the label 'Nuclear power plants' on top and 'Splitting of atoms' within it. The overlapping portion has the label P inside it.

Which of the following best describes the process labeled P?

Absorption of radioactive material
Cooling of reacting atoms
Production of water
Release of energy