Hey there Chainsmokers!
A nuclear fusion would actually be known to be a (reaction) of a very low fuse. Which on this case, it would then carry alot of energy, why? This would happen because the fuse would then form heavier substances such as nucleas.
So, from looking at your options listed above, it would seem that the correct answer would be your option "a".
"the process of two or more atomic particles sticking together to form a heavier atomic nucleus.".
Your correct answer would be option a.)
Hope this helps you dear!