the controlled release of nuclear energy in a reactor is accomplished by:

a)allowing the critical mass of fuel to react
b)controlling a chain reaction
c)controlling fission without a chain reaction
d)all of the above

I believe the answer is C

Explanation:

C) controlling fission without a chain reaction

Explanation:

Because

If a chain reaction occurs, then the amount of energy would increase exponentially, so in order to monitor the release of energy, fission must be controlled without controlling a chain reaction.  

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