Question: Among the universities with a score in teaching of over 90 in 2011, what is the percentage of those in the United States of America?
SQL: SELECT CAST(SUM(CASE WHEN T4.country_name = 'United States of America' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) AS per 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 INNER JOIN country AS T4 ON T4.id = T3.country_id WHERE T1.criteria_name = 'Teaching' AND T2.year = 2011 AND T2.score > 90