Among the easiest courses, what is the name of the course where most students got an A?
diff refers to difficulty; the easiest courses refers to diff = 1; A refers to an excellent grade in which grade = 'A' for the course;
SELECT T2.name FROM registration AS T1 INNER JOIN course AS T2 ON T1.course_id = T2.course_id WHERE T1.grade = 'A' AND T2.diff = 1 GROUP BY T2.name ORDER BY COUNT(T1.student_id) DESC LIMIT 1