American美国人是可数名词。
American：n.美洲人；(尤指)美国人；美国英语；
American的复数形式是Americans
It is interesting to contrast the British legal system with the American one.
把英国的法制与美国的加以对比很有意思。
North American literature is the main theme of this year's festival.
北美文学是今年艺术节的主题。
He developed his own program in partnership with an American expert.
他与一位美国专家合作开发出自己的程序。
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