资料题：The passage mainly discusses about（　）。

Very few people were coming to eat at the White Rose restaurant, and its owner didn't know what to do.The food in his restaurant was cheap and good, but nobody seemed to want to eat there.Then he did something that changed all that, and in a few weeks his restaurant was always full of men and their lady friends.Whenever a gentleman came with a lady, a smiling waiter gave each of them a beautiful menu.The menu looked exactly the same on the outside.but there was an important difference inside.The menu that the waiter handed to the man gave the correct price for each dish and each bottle of wine; while the menu that he handed to the lady gave a much higher price! So when the man calmly ordered dish after dish and wine after wine, the lady thought he was much more generous than he really was.