找到英文版的答案了,谁翻译下
To be a public good, a good must be neither rival nor excludable. When the Internet isn’t congested, it is not rival, since one person’s use of it does not affect anyone else. However, at times traffic on the Internet is so great that everything slows down¾at such times, the Internet is rival. Is the Internet excludable? Since anyone operating a Web site can charge a customer for visiting the site by requiring a password, the Internet is excludable. Thus the Internet is not strictly a public good. Since the Internet is usually not rival, it is more like a natural monopoly than a public good. However, since most people’s Web sites contain information and exclude no one, the majority of the Internet is a public good (when it is not congested).