Answer:
B. Developing a theory
Step-by-step explanation:
I believe the answer to be B because it is the beginning of a describing why the color of light affects the rate of plant growth but it is not a full theory yet. It cannot be D o A because there is no experiment being done or a conclusion to be made yet. It is also not C because the sentence does not fit the formatting of a hypothesis. A hypothesis is when you say "if this happens.....this will follow" and in this sentence there is no if, then structure.