Correct Option: D

A thermonuclear weapon is a nuclear weapon design that uses the heat generated by a fission bomb to compress a nuclear fusion stage which indirectly results in greatly increased energy yield (i.e., bomb “power”). It is colloquially referred to as a hydrogen bomb or H-bomb because it employs hydrogen fusion, though in most applications the majority of its destructive energy comes from uranium fission, not hydrogen fusion by itself. The fusion stage in such weapons is required to efficiently cause the large quantities of fission characteristic of most thermonuclear weapons. The concept of the thermonuclear weapon was first developed and used by the United States and has since been used in most of the world’s nuclear weapons.