Provide the score of the most populated university in 2011.
most populated university refers to MAX(num_students); in 2011 refers to year = 2011;
SELECT T2.score FROM university_year AS T1 INNER JOIN university_ranking_year AS T2 ON T1.university_id = T2.university_id WHERE T1.year = 2011 ORDER BY T1.num_students DESC LIMIT 1