Answer the following question given this paragraph: 

Unfortunately, using energy from nuclear fusion is far from a reality. Scientists are a long way from developing the necessary technology. One problem is raising temperatures high enough for fusion to take place. Another problem is that matter this hot exists only in the plasma state. There are no known materials that can contain plasma, although a magnet might be able to do it. That’s because plasma consists of ions and responds to magnetism. You can learn more about research on nuclear fusion at the URL below.


Q: In which state does matter need to be for nuclear fusion?


A:
plasma state