Answer:
the cost of using fusion in a practical way is too high.
Step-by-step explanation:
When two smaller unstable nuclei combine to make a stable nuclei then this process of stability of nuclei is known as nuclear fusion.
In this process of nuclear fusion the energy is released due to stability but in this process the initial energy is required to start the reaction.
This process of starting the reaction is relatively of high cost as compare to nuclear fission reaction.
So here correct answer will be
the cost of using fusion in a practical way is too high.