I believe it is A. Teacher because that is a career.
The answer is high pressure. In a nuclear reaction process, high temperature and high pressure is required for turning hydrogen nuclei into a helium nucleus. It is impossible for it to happen simultaneously because it requires tremendous amounts of energy. Extreme conditions are required for the atoms to overcome electrostatic repulsion.
The correct answer is- Proton
A proton is approximately 2,000 times heavier than an electron. In most cases, atoms have an equal number of protons and electrons. However, because protons are so much heavier than electrons, the electrons do not make a significant contribution to the mass of an atom.