What is the primary source of energy in the sun? 

A)  magnetism 
B)  gravity 
C)  nuclear fusion 
D)  nuclear fission

The primary source of energy in the sun is nuclear fusion, where hydrogen atoms combine to form helium and release huge amounts of energy in the process. This process requires extremely high temperatures and pressures, which are only found at the core of the sun. Magnets and gravity play important roles in the movement and stability of the sun, but they are not the primary source of energy. Nuclear fission, on the other hand, involves splitting atoms to release energy, which is not the process that powers the sun.