Answer:
B
Step-by-step explanation:
D: Not the choice. A theory is a guess at how something works. It suits the evidence but is not proven.
C: An observation is just that. An observation. If I say the sky is blue, your response is likely so what?
A: a hypothesis is a formal theory. You are in the process of setting up a test of some kind. Not A
The answer is B. That pretty much locks in the result.