what are the top three drugs most often prescribed for patients of the age 20s in 2101?
select t1.drug from ( select prescriptions.drug, dense_rank() over ( order by count(*) desc ) as c1 from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.age between 20 and 29 ) and strftime('%y',prescriptions.startdate) = '2101' group by prescriptions.drug ) as t1 where t1.c1 <= 3