CREATE TABLE table_name_50 (airing_date VARCHAR, english_title__chinese_title_ VARCHAR, genre VARCHAR, official_website VARCHAR, number_of_episodes VARCHAR)
What's the airing date of Armed Reaction 陀槍師姐 with 20 episodes in the Modern Action genre having an official website?
SELECT airing_date FROM table_name_50 WHERE official_website = "official website" AND number_of_episodes = 20 AND genre = "modern action" AND english_title__chinese_title_ = "armed reaction 陀槍師姐"