A、In America. B、In the Center of America. C、In South America. D、In North America. D由“all those giant creatures，the Metgauna of N

Narrator:
    Listen to part of a lecture in an archaeology class.
Professor:
    Between 11, 000 and 10, 000 B. C. E., North America was populated by a wide variety of great beasts, like mammoth and mastodons, both elephant-like creatures with big tusks, and camels, giant sloths, the list goes on. By about 10,000 B. C. E., all those giant creatures, the Metgauna of North America were gone. We don’t know exactly what happened to them, but there are some theories. One theory is that they were hunted to extinction by humans. The humans who coexisted with these giant species in North America at that time were what we today called the Clovis People. And there is a Clovis site in a valley in Southern California where the remains of thirteen mammoths were found. And spear points, tools for processing meat, and fire places. That would appear to be some pretty compelling evidences. Mammoth bones have also been found at some other Clovis sites. But then at other Clovis sites, there’s also a lot of evidence that the Clovis people mostly gather plants and hunted small game, like rabbits and wild turkeys. Also there are several places in North America where you have natural accumulations of mammoth bones that look very similar to the accumulations at the Clovis site, except there’s no human debris, where the mammoth almost certainly died as a result of some kind of natural disaster. So I think it is quite likely that those thirteen mammoths in Southern California also died of natural causes, and that the Clovis people simply took advantage of the situation. That’s the hunting theory.
20. Where was the Metgauna before the disappearance?
21. Why does the professor mention an archaeological site in Southern California?
22. What is the professor’s opinion about the Clovis people?