One challenge when researching whether holding elected office changes a person's behavior is the problem of ensuring that the experiment has an appropriate control group. To reveal the effect of holding office must compare people who hold elected office with people who do not hold office but who are otherwise similar to the office-holders. Since researchers are unable to control which politicians win elections, they therefore __ (1) Mark for Review Which choice most logically completes the text? A struggle to find valid data about the behavior of politicians who do not (A) currently hold office. B can only conduct valid studies with people who have previously held office rather than people who presently hold office. C should select a control group of people who differ from office holders in C several significant ways. D will find it difficult to identify a group of people who can function as an appropriate control group for their studies.