Passage 1Nuclear power is obtained from the energy which can be released from nucleus of an atom. Until the twentieth century man used water, wood and the fossil fuels (coal, oil and gas) as sources of power. During the first quarter of the twentieth century physicists investigated the structure of the atom. In 1919 Rutherford split the atom artificially. Thirteen years later, the neutron was discovered. In 1939 Hahn and Strassman investigated the action of neutrons on uranium-235. They found that it was split into two equal pieces. This process is known as fission. It releases great amount of energy. The neutrons that are released in fission produce fissions in other atoms. This is known as a chain reaction. On 2nd December 1942 Enrico Fermi and his colleagues produced the first controlled nuclear chain reaction. Since then atomic energy has been used in war and peace. In 1951 electricity was first produced by using the heat from a nuclear reactor. More and more countries are building nuclear power stations to produce electricity. The neutrons that are released in fission produce fissions in other atoms, this is known as ().

A. split
B. fission
C. chain reaction
D. atomic energy