Answer: Method B is an experiment because it randomly assigns volunteers a sunscreen, while method A is an observational study.
Explanation:
Based on the information given, we can infer that method A is an observational study. An observational study simply refers to the study whereby the researchers just observe the impact of a rise factor without them trying to change the people or things exposed to it. This can be seen as the survey adults visited the beach on the busy weekend asking each adult the brand of sunscreen that they use and then assess their arms for sun exposure.
Method B is an experiment. An experiment refers to a test that's carried out in order to evaluate a particular hypothesis or theory. Method B is an experiment because it randomly assigns volunteers a sunscreen.
Therefore, the correct option is D.