"You are swimming today."
Translation:आप आज तैर रहे हैं ।
Sentences become plural in Hindi when you are wishing to convey respect when talking about someone, or when you use आप or तुम, the sentence is conjugated in the plural, hence रहे हैं instead of रहा है
I put तुम आज तैर रहा हो and was marked wrong. I think that answer should be accepted as far as I can tell, though if there is a reason it is not correct I’d be happy to hear it.