Answer:
D
Step-by-step explanation:
Since this is a biology/chemistry question, you have to be careful that you use the right term. You must be talking about atoms. So B and C are both incorrect because the word cell is used as the main location.
What about A and D? The atom is used and those two are the ones you need to consider. A neutron gives its home address as the nucleus. It is part of the nucleus. So A is incorrect. A neutron is inside the nucleus.
That leaves with D and that's the answer.