A.SELECT 姓名 FROM 读者 WHERE NOT EXISTS; (SELECT 借书证号 FROM 借阅 WHERE 借阅.借书证号=读者.借书证号) B.SELECT 姓名,借书证号 FROM 读者 WHERE (SELECT*FROM 借阅 WHERE 借阅.借书证号=读者.借书证号) C.SELECT 姓名,借书证号 FROM 读者 WHERE NOT EXISTS; (SELECT*FROM 借阅 WHERE 借阅.借书证号=读者.借书证号) D.SELECT 姓名,借书证号 FROM 读者 WHERE 借阅=NULL (SELECT*FROM 借阅 WHERE 借阅.借书证号=读者.借书证号)