For each of the research questions below, identify the appropriate observational unit and variable. (a) You are interested if the proportion of American citizens who have a passport is over 30%. Observational Unit: |[ Select ] C Variable: [ Select ] (b) You are interested if those who train for their first marathons lose more than 10 pounds on average over the course of their training period. Observational Unit: |[ Select ] Variable: [ Select ] C (c) You want to know if the 5 year graduation rate (the % of students who enroll at a college and complete their degree within 5 years) of a certain college is above 80%. Observational unit: [ Select ] C Variable: [ Select ] C