Among the race of all students, what is the control of institution and level of institution with highest number of students?
highest number of students refers to student_count; all students refer to race = 'X'.
SELECT DISTINCT T1.control, T1.level FROM institution_details AS T1 INNER JOIN institution_grads AS T2 ON T2.unitid = T1.unitid WHERE T2.race = 'X' AND T1.student_count = ( SELECT MAX(T1.student_count) FROM institution_details AS T1 INNER JOIN institution_grads AS T2 ON T2.unitid = T1.unitid WHERE T2.race = 'X' )