May: There are so many people that the tickets are all sold out!

Daniel: Luckily we got the last two.

May: Look, Danny. The Four Great Inventions!

Daniel: Gunpowder, compass, the paper making, and the printing.

May: I really admire those who made such great inventions!

Daniel: May, I don't see why they are great. They are just simple things.

May: They look simple today. But they were milestones in their times.

Daniel: Milestones? May, you must be kidding.

May: Just think Bill Gates, those inventions are as important as the windows system.

Daniel: Well, I suppose the ancient inventors made a lot of money out of them.

May: No, quite the contrary.

Daniel: Why? Didn't you say that they were milestones?

May: Yes, but they went to the public without any patent protection.

Daniel: Well, their inventors were not as clever as Bill Gates.