Determine whether the study depicts an observational study or an experiment. Sixty patients with vision loss are divided into two groups. One group is treated with experimental surgery. The other is not. After one month, both groups are questioned about their ability to read. XX Is the study an observational study or an experiment? OA. The study is an experiment because the study examines individuals in a sample, but does not try to influence the variable of interest. OB. The study is an experiment because the researchers control one variable to determine the effect on the response variable. OC. The study is an observational study because the study examines individuals in a sample, but does not try to influence the response variable. OD. The study is an observational study because the researchers control one variable to determine the effect on the response variable.