Final answer:
Research questions are about a population but are studied using a sample, with d) Population, sample being the correct answer.
Step-by-step explanation:
Although research questions usually concern a population, the actual research is typically conducted with a sample. The correct answer to the question is d) Population, sample.
A population is the overall group of individuals that the researchers are interested in, while a sample is a subset of that population chosen to represent it in the study. A parameter is a characteristic or measure obtained by using all members of a population, whereas a statistic is a characteristic or measure obtained by using only the sample. The success of a study greatly depends on how well the sample represents the population to provide an accurate estimate of the population parameter through statistical analysis.