The correct answer is: 'Emilian will teach the Americans'. The -wa- infix makes it specific.
Not necessarily. There's a general tendency for object prefixes to be more likely to be used more when the object is specific, or when the object is animate. Neither of these is a completely hard and fast rule for actual Swahili use.
But surely "Emilian teaches the Americans should be accepted"?
No, because of the future tense marker infix "ta".
Emilian will teach Americans was marked wrong without the word the.
I also think this should be right