Video hướng dẫn viết chữ ghi âm r: https://www.youtube.com/watch?v=wxBBjCF4jqo&pp=ygUjaMaw4bubbmcgZOG6q24gdmnhur90IHIgcuG7lSB0ciB0cmU%3D
Video hướng dẫn viết chữ ghi âm tr: https://www.youtube.com/watch?v=8O89jL2bcVE&list=PLE8HqJ5ZvFuynhVGE95mIxyo6CcBmrn54&index=11&pp=iAQB