Answer:
A. consult multiple sources to validate the theory
Step-by-step explanation:
When we search for something, we may find research sources that show incorrect information. For this reason, the idea is that you use various sources of research, so that one validates the information of the other and you can do a quality research and committed to the truth.
That is what Robert must do. That's because he has two research sources that are showing controversial information about how Amelia Earhart died. Then he should search more sources of research on Amelia Earhart and see the information they have in common.