https://www.jiji.com/sp/article?k=2019031900060&g=spo
https://www.bloomberg.co.jp/news/articles/2019-03-19/POLB656JIJUO01
https://diamond.jp/articles/-/197144?display=b
https://www.nikkansports.com/m/entertainment/akb48/news/amp/201903190000283.html