They must be Americans.
They don't seem to be Americans.
He doesn't seem to be an American.
She doesn't seem to be an American.
They don't seem to be Americans.
It does not seem to be an American.
The Americans had nothing to do with the matter.
Are they American?
He doesn't seem to be an American.
She doesn't seem to be an American.
an American (especially to non-Americans)
I understand you're visiting from America.
As far as I know, he is American.
I am an American.