I thank you 和 thank you 和 thank you very much 和 I thank you very much 和 <s>thank you pretty much</s> 的差別在哪裡？如果不好說明，請提供一些例句。

thank you pretty much is a phrase I've never heard, so that's a bit unnatural, as for the others, "thank you" on its own is pretty standard, "thank you very much" is a bit longer to say, so tends to be used to express more than the standard level of gratitude. "I thank you" is a bit old fashioned, so I know I usually use it in a playful manner with friends