Done 3 of 3 Does donating blood lower cholesterol levels? Fifty sets of identical twins were recruited for the study. For each set of twins, one twin was randomly assigned to give blood once a month for 12 months. The other twin was prohibited from giving blood during the 12 month period. For each participant, cholesterol tests were given at the end of the 12 month study period. Which of the following best describes the data collected? This is an observational study that collected paired data. O This is a retrospective observational study that contains data on two separate groups. O The data collected was from a stratified random sample. This is an experiment that collected paired data