Tôi muốn viết ở đây thêm một lần nữa. Xin cám ơn mọi người đã giúp tôi học tiếng Việt! P/S: In my opinion, it is due to cultural thing: when people want to say thanks to some one who helps them, they say thanks to every one. People don't want to specify who helps them and who does not help them. Except for one case, you want to say thanks to only one special person who helps you, you can use the structure "người mà"