Which district has the most accounts with loan contracts finished with no problems?
status = 'A' refers to loan contracts finished with no problems
SELECT T1.district_id FROM district AS T1 INNER JOIN account AS T2 ON T1.district_id = T2.district_id INNER JOIN loan AS T3 ON T2.account_id = T3.account_id WHERE T3.status = 'A' GROUP BY T1.district_id ORDER BY COUNT(T2.account_id) DESC LIMIT 1