"The boy eats a sausage."
Translation:Το αγόρι τρώει ένα λουκάνικο.
Duolingo often throws in a sentence irrelevant to the topic of the lesson studied. I've seen this numerous times in this and other courses too.
Using hints on hover, I saw "το" as an option for "one"... I thought" το" was used only as the definite article, "the". Is this a mistake in the exercise, or a valid usage?
I don't see "one" in the hints there right now.
However, remember that hints are not sentence-specific -- a given word will always show the same hints no matter which sentence it's in. So some of the hints may not apply to a word in the sentence you are looking it.
To address two other points:
- το can be not only the definite article, but also a short-form direct object pronoun, e.g. το βλέπω "I see it" (here το represents the object "it").
- I can't think of a context where the Greek sentence has το in it and a good English translation would have "one" in it. But I'm not willing to rule out such a sentence categorically. (Especially since the usage of definite and indefinite articles is not identical in the two languages.)