Regarding nuclear reactions that release a great deal of energy,

Question

which statement is true?
A. In a fission chain reaction, a uranium nucleus struck by a
high-energy neutron emits two neutrons.
B. Nuclear fission releases more energy per unit mass than
does a fusion reaction.
C. Nuclear reactors produce dangerous levels of air pollution.
D. A fusion reaction proceeds through the joining of two
isotopes of hydrogen

I think it's D