Questions 21 to 25 are based on the following passage.Could you reproduce Silicon Valley elsewhere, or is there something unique about it?It wouldn't be surprising if it were hard to reproduce in other countries, because you couldn't reproduce it in most of the US either. What does it take to make a Silicon Valley?It's the right people. If you could get the right ten thousand people to move from Silicon Valley to Buffalo, Buffalo would become Silicon Valley.You only need two kinds of people to create a technology hub (中心): rich people and nerds (痴迷科研的人).Observation bears this out. Within the US, towns have become startup hubs if and only if they have both rich people and nerds. Few startups happen in Miami, for example, because although it's full of rich people, it has few nerds. It's not the kind of place nerds like.Whereas Pittsburgh has the opposite problem: plenty of nerds, but no rich people. The top US Computer Science departments are said to be MIT, Stanford, Berkeley, and Carnegie-Mellon. MIT yielded Route 128. Stanford and Berkeley yielded Silicon Valley. But what did Carnegie-Mellon yield in Pittsburgh? And what happened in Ithaca, home of Cornell University, which is also high on the list?I grew up in Pittsburgh and went to college at Cornell, so I can answer for both. The weather is terrible, particularly in winter, and there's no interesting old city to make up for it, as there is in Boston. Rich people don't want to live in Pittsburgh or Ithaca. So while there're plenty of hackers (电脑迷) who could start startups, there's no one to invest in them.Do you really need the rich people? Wouldn't it work to have the government invest in the nerds? No, it would not. Startup investors are a distinct type of rich people. They tend to have a lot of experience themselves in the technology business. This helps them pick the right startups, and means they can supply advice and connections as well as money. And the fact that they have a personal stake in the outcome makes them really pay attention.What do we learn about Silicon Valley from the passage?