Hey! I took the Penn foster exam, and i answered (a). I got it wrong, so I tried to find the correct answer. I’m pretty sure the answer is (b), and here’s some text from the Penn foster lesson.
“Unfortunately, nuclear fusion can't be used in nuclear power plants as the energy required to start a fusion is very large. The energy required to start a fusion reaction cannot be generated in a controlled manner.”
Anyways, hope this helps:) If this is wrong, please comment and tell me the correct answer.