Among the universities with a score in teaching of over 90 in 2011, how many of them are in the United States of America?
in 2011 refers to year 2011; in teaching refers to  criteria_name = 'Teaching'; score in teaching of over 90 refers to score > 90; in the United States of America refers to country_name = 'United States of America';
SELECT COUNT(*) FROM ranking_criteria AS T1 INNER JOIN university_ranking_year AS T2 ON T1.id = T2.ranking_criteria_id INNER JOIN university AS T3 ON T3.id = T2.university_id WHERE T1.criteria_name = 'Teaching' AND T2.year = 2011 AND T2.score > 90