Answer:it’s most likely A
Sorry if I’m wrong
Answer: It's an EXPERIMENT
Explanation: Experiment is done when we apply anything to a samples or conditions in other to study another sample or conditions.
Observation is done when, we study samples or conditions in it's natural way, without application of anything that may alter it's result.
Because the researcher has applied fertilizer to one side and did not apply to the other side, that means he has performed an experiment. Since he wasn't observing the two sample in it's natural way without any external application.
