what was the drug that patient 5905 had been prescribed two times until 10/2101.
select t1.drug from ( select prescriptions.drug, count( prescriptions.startdate ) as c1 from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 5905 ) and strftime('%y-%m',prescriptions.startdate) <= '2101-10' group by prescriptions.drug ) as t1 where t1.c1 = 2