"What are you drinking, milk?"
Translation:Что это ты пьёшь, молоко?
Happened to me, too. I've only encountered the пьёт lesson and then this one came out of left field. Had to guess but got it wrong. Duo should introduce the translation texts first (where there are hover hints) before the corresponding multiple choice questions. Otherwise, there's really no way but to guess the answer to sentences you see for the first time.