Imagine we have the two datasets below (the first named person_age.dta and the second rent.dta) person_id county_id age 1 1 1 48.37863 23 2 2 2 39.79116 3 3 3 59.02524 4 4 4 40.65527 5 6 56 7 7 8 8 1 29.78645 2 3 52.80093 4 52.46461 county_id average_rent 55.16973 1 1 1348.872 2 2 1266.886 3 3 1136.646 4 4 1028.557 If we first load in person_age.dta and then merge to rent.dta, the correct code from the merge command would be