Database: thrombosis_prediction
Question: For laboratory examinations take in 1984, list all patients below 50 years old with normal platelet level.
SQL: SELECT DISTINCT T1.ID FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID WHERE T2.PLT BETWEEN 100 AND 400 AND STRFTIME('%Y', T2.Date) - STRFTIME('%Y', T1.Birthday) < 50 AND STRFTIME('%Y', T2.Date) = '1984'