The correct option is D All of the above
In an uncontrolled chain reaction, the reaction occurs rapidly so that the energy is released instantaneously and therefore, we can't convert any of that into any useful form of energy.
In a controlled chain reaction, we can control the speed of reaction and thereby control the rate of release of energy. Due to this, we can convert it into any other useful form of energy.
Hence, (D) is the correct answer.