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.