Help with parts a,b,c,d

Problem #1 On April 29, 2020, Pfizer started the clinical trial to evaluate the safety, tolerability, immunogenicity, and efficacy of SARS-COVZ RNA vaccine candidates against Covid-19 in healthy individuals. Around 44000 individuals 12 years and older participated in the study, each of which was randomized into placebo or experimental groups. Neither the participants nor the investigators know what group each participant was assigned into. At the end of Phase 1, the safe dosage level of the vaccine was determined. Some of the variables collected are Gender (Male/ Female), Age in years, and dosage received (Low, low-mid, mid). (source: https: [ Z clinicaltrialsgovz thZ showz N CT04368728). a. Is this an observational or experimental study? Justify your choice. b. Is the study single blind or double blind? Explain. c. In graphically presenting the ages (in years) of the participants, which graph(s) that we discussed in class can be used? d. What type of variable dosage received is, and what is its level of measurement