Scientific evidence collected and observed by scientists over time suggests that the atom has a nucleus, containing protons and neutrons, and electrons that surround the nucleus. What makes this a scientific theory? a. It is built on investigations by many scientists in order to provide a strong and testable explanation. b. It has been proven by several scientists independently, resulting in its being accepted as truth. c. It is based on the beliefs and opinions of the majority of the scientific community. d. It has been proven to be scientific fact through all the experiments and investigations.