"None of them are American."
If you left 都 out, the sentence would make perfect sense but the meaning would change slightly, it'd be something like "They aren't American." 他们都是美国人 - They are all Americans / All of them are Americans. 他们都不是美国人 - They are all not Americans / None of them are American.
都 generally means "all", but when it's followed by a negative word like 不 or 没, it means "none".
Hi Duo, I don't know where to put this request but please let us review the pronunciation of the correct phrases in these Discussion pages, just as in the other language courses. Since Chinese is a tonal language, hearing the sentences and associating the tones for each word is the best way to learn it. I hope the moderators can read this, it'll help us a lot. Thanks.
Weird. I was corrected on this sentence when I had written exactly the same thing. I've checked several times. First time this has ever happened
It says in correcting: "You used the wrong word" with the following characters: 他们都不是美国人。
But in my answer I had written: 他们都不是美国人。