instruction: when was patient 51977 prescribed a potassium chloride and diltiazem at the same time for the last time in 02/last year?
response: SELECT t1.startdate FROM (SELECT admissions.subject_id, prescriptions.startdate FROM prescriptions JOIN admissions ON prescriptions.hadm_id = admissions.hadm_id WHERE prescriptions.drug = 'potassium chloride' AND admissions.subject_id = 51977 AND DATETIME(prescriptions.startdate, 'start of year') = DATETIME(CURRENT_TIME(), 'start of year', '-1 year') AND STRFTIME('%m', prescriptions.startdate) = '02') AS t1 JOIN (SELECT admissions.subject_id, prescriptions.startdate FROM prescriptions JOIN admissions ON prescriptions.hadm_id = admissions.hadm_id WHERE prescriptions.drug = 'diltiazem' AND admissions.subject_id = 51977 AND DATETIME(prescriptions.startdate, 'start of year') = DATETIME(CURRENT_TIME(), 'start of year', '-1 year') AND STRFTIME('%m', prescriptions.startdate) = '02') AS t2 ON t1.subject_id = t2.subject_id WHERE DATETIME(t1.startdate) = DATETIME(t2.startdate) ORDER BY t1.startdate DESC LIMIT 1