A researcher,interested in testing a new COVID-19 vaccine, needs to determine whether the vaccine is effective and can produce antibodies against SARS-COV-2. To test the vaccine, the researcher recruits a sample of participants (at random) from Philadelphia and randomly assigns them to either a experimental vaccine group or to a placebo group. Blood antibodies are then tested for all participants 8 weeks later. Based on this case scenario, which of the following research designs best describe the kind of study conducted to answer the research question?