Give the full name and capability of students who failed in any courses.
full name of students = f_name, l_name; failed refers to grade IS NULL;
SELECT T2.f_name, T2.l_name, T1.capability FROM RA AS T1 INNER JOIN student AS T2 ON T2.student_id = T1.student_id INNER JOIN registration AS T3 ON T2.student_id = T3.student_id WHERE T3.grade IS NULL OR T3.grade = ''