According to the nebular hypothesis, when did nuclear fusion begin?

After the planets formed.

When the sun was 5 billion years old.

When the nebula first exploded outward into space.

When particles were pulled together so tightly they combined.

Question

According to the nebular hypothesis, when did nuclear fusion begin? 

 After the planets formed. 

 When the sun was 5 billion years old. 

 When the nebula first exploded outward into space. 

 When particles were pulled together so tightly they combined.

unklerhaukus · Answer

fusion is two atoms becoming one

anonymous · Answer

so what is the answer??