In the process of nuclear fusion, large amounts of energy, at temperatures of approximately 120 million kelvin, are required to join two nuclei into a single, heavier nucleus. why does the process of fusion require so much energy in order to take place?
a) to allow the electrons to enter the nucleus
b) to remove the electrons from the electron clouds
c) to cause the two nuclei to slow down and find each other
d) to overcome the electrostatic forces between opposing nuclei