John Dalton proposed that all matter is composed of very small things which he called atoms. This was not a completely new concept as the ancient Greeks (notably Democritus) had proposed that all matter is composed of small, indivisible (cannot be divided) objects. When Dalton proposed his model electrons and the nucleus were unknown.
I had to look for the options and here is my answer: The two requirements for nuclear fusion that are needed to be met in order for the elements hydrogen and helium fuse to make heavier elements are extremely high temperatures and density. Hope this helps.
