Which statement about nuclear fusion is correct? 

A)  High-temperature fusion is much harder to initiate but releases more energy per unit of fuel than fission. 
B)  During nuclear fusion, more than two nuclei of isotopes of light elements are forced together at high temperatures until they fuse and absorb energy. 
C)  Controlled nuclear fusion reactors are being tested in California and will probably be ready to come online by the year 2030. 
D)  Fusion is the source of energy in the soil.

Nuclear fusion is the process of combining two atomic nuclei to form a heavier nucleus, which releases enormous amounts of energy in the form of light and heat. High-temperature fusion requires immense heat to initiate the fusion process, but it releases more energy per unit of fuel than fission. In contrast, fission involves splitting the atomic nucleus into two smaller nuclei, which releases a lower amount of energy. Option B is incorrect as during nuclear fusion, only two nuclei of isotopes of light elements are forced together at high temperatures until they fuse and release energy. Option C is also incorrect as although scientists are working on developing controlled nuclear fusion reactors, they are still in the experimental stage, and it is not certain when they will be ready for commercial energy production. Option D is completely unrelated to nuclear fusion and is incorrect.