"Những con khỉ ăn chuối."

Translation: The monkeys eat bananas.

[Remysss]

"Monkeys eat banana." should be accepted.

[JCMcGee]

why doesn't "chuối" have/need a "những" before it?

Does this sentence not say: "Monkeys eat banana"?

[LanguageButcher]

For nouns with one syllable, you can safely ignore the classifier. It sort of acts like a compound verb -like bird-watching. We don't know how many birds you watch, but that's what you do - bird watch. So ăn cơm = eat rice (have dinner), mặc áo = put on a shirt, etc.