資料： https://en.wikipedia.org/wiki/Hippopotamushttps://ja.wikipedia.org/wiki/%E3%82%AB%E3%83%90https://www.thoughtco.com/hippo-facts-4142336https://www.livescience.com/27339-hippos.htmlhttps://a-z-animals.com/animals/hippopotamus/
http://www.nicovideo.jp/watch/sm41824800
