谢谢龙先生用英语怎么说

"Thank you, Mr. Long" is the correct way to say "谢谢龙先生" in English. "Thank you" is a common phrase used to express gratitude in English, and "Mr. Long" is the English equivalent of "龙先生". Here are a few example sentences and their translations:

"Thank you, Mr. Long, for your help." (谢谢龙先生，你的帮助。)
"I would like to express my gratitude to Mr. Long for his generous donation." (我想向龙先生表示感谢他慷慨的捐赠。)
"Thank you, Mr. Long, for being such a great teacher." (谢谢龙先生，你是一个伟大的老师。)

The phrase "thank you" is derived from the Old English phrase "þancian", which means "to think, to be grateful". It is a common phrase used in many languages to express gratitude and is often used in both formal and informal settings.