How about "yes, let's go!"
That's better of the given translation, I'd say.
Any of these answers are equally correct.
i agree. this should be corrected.
This must be corrected! "Sí, " does not determine anything, all the answers are correct!
What's wrong with "Yes, come on"
In my experience so far, duolingo always indicates an imperative with an exclamation mark, so if that isn't there, a present tense translation is expected.