Researchers wanted to determine if having a refrigerator in the bedroom is associated with obesity. The researchers administered a questionnaire to 384 twelve-year-old adolescents. After analyzing the results, the researchers determined that the body mass index of the adolescents who had a refrigerator in their bedroom was significantly higher than that of the adolescents who did not have a refrigerator in their bedroom. Complete parts (a) through (e) below. B. The researchers administered a questionnaire to obtain their data without trying to influence an explanatory variable of the study. C. The researchers tried to influence the outcome of the study. OD. The researchers observed the behavior of the individuals in the study without trying to influence an explanatory variable of the study. What type of observational study , this? Case-control study O Cross-sectional study O Cohort study