D is the answer to this question. Do you know that the margin of error can be lessened when you increase your sample size? Just remember that you need to take note of the different factors that may affect your study. The alpha and the beta are going to be extremely important.
The alpha refers to the level of probability that can be accepted as true that is not due to chance. Beta, on the other hand, refers to the possibility of detecting a potential change if there is going to be changed based on what is being studied. A well-made and well-researched study can potentially provide the information that people need.