In which country does the most populated university in 2014 located ?
the most populated university refers to max(num_students); in 2014 refers to year = 2014
SELECT T2.country_id FROM university_year AS T1 INNER JOIN university AS T2 ON T1.university_id = T2.id WHERE T1.year = 2014 ORDER BY T1.num_students DESC LIMIT 1