How many athlete from China participate in the 2016 Summer Olympics?
athletes from China refer to person_id where region_name = 'China'; the 2016 Summer Olympics refer to games_name = '2016 Summer';
SELECT COUNT(T3.id) FROM games AS T1 INNER JOIN games_competitor AS T2 ON T1.id = T2.games_id INNER JOIN person AS T3 ON T2.person_id = T3.id INNER JOIN person_region AS T4 ON T3.id = T4.person_id INNER JOIN noc_region AS T5 ON T4.region_id = T5.id WHERE T1.games_name = '2016 Summer' AND T5.region_name = 'China'