I believe the answer is D.
I believe the medulla is the answer.
Answer:
i think b is the answer hope this helps:))
Explanation:
An atom is a particle of matter that uniquely defines achemical element. An atom consists of a central nucleus that is usually surrounded by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons
