<span>the intellectual and practical activity encompassing the systematic study of the structure and behavior of the physical and natural world through observation and experiment.
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The correct answer is D. for sure.
<span>Answer: a. take place in nuclear reactors
</span><span>Controlled nuclear chain reactions are the reaction in nuclear reactors. The reaction is controlled to make its rate slower. This will make the reaction relatively safer, so the energy produced can be changed into electricity in power plant. When the reaction is not controlled, it could cause explosive like in nuclear bomb.</span>