Answer:
Option A
Option B
Step-by-step explanation:
It isn't option D because electrons are on the outside of the nucleus of the atom, and it isn't option C because isotopes are usually the same elements but with different amounts of neutrons while having the same number of protons. Leaving options A and B or "neutrons and protons" as your answer and that's because neutrons and protons are always found in the center of the nucleus which also helps determine the element.
Hope this helps.