Answer b answer analysis test analysis: this question comprehensively examines knowledge. There are four options for the topic, and four aspects of knowledge are examined. However, what we examine is the understanding of basic concepts and laws. As long as the relevant concepts in the textbook are correctly understood, the solution: A and β decay is that a neutron in the nucleus becomes a proton and an electron is released at the same time, so A is wrong; B, cadmium has a large neutron absorption interface, so it is used to absorb neutrons produced by fission, so B is correct; C, fusion must be carried out at high temperature, so C is wrong; D, nuclear fusion and nuclear fission mostly release nuclear energy, and only a few nuclear reactions absorb energy, so D is wrong; Therefore, students are prone to make mistakes in the process of answering questions like this. As long as they fully understand the relevant concepts in the textbook, they can answer correctly.