c) Nuclear energy

Nuclear fusion and nuclear fission are both sources of nuclear energy. Nuclear fission occurs when uranium atoms are attacked by low-energy neutrons, causing the atom to divide into two lighter nuclei. Lighter nuclei are fused together to form a relatively heavier nucleus in nuclear fusion. Nuclear reactions produce enormous amounts of energy and can be carried out in the absence of sunlight.

Geothermal energy is obtained from the deep stored energy in the form of heat in the earth’s crust. The uneven heating of the earth’s surface results in wind movement and bio-mass is obtained from the dead remains of the plants and the animals.