Again, dubious choice of selection/candidate words. It asks me to chose between ”beai”, ”bea” and ”beați”, but the answer "voi bea apă rece" is also grammatically correct, even if it has a different meaning (I will drink cold water).
In this sentence, voi is a personal pronoun. The voi you are talking about is an auxiliari verb coming from the word to want - a vrea
Maybe the English, "... had been drinking ..." approximates the Romanian, "... beați ..."?
That had+continuous form always confuses me... I have to think to ”you had worked” versus ”you have been working”, or so... But you know better how to translate it, if it shows an action started in the past, and finished in the past before another action started and finished in the past too, then it is more like "băuseți/băuserăți".
”Beați” shows an action started in the past, but not necessarily finished when another action started in the past, about whose end (or not) we don't know. For which the proper translation is the one given by Duo. You were drinking cold water when we arrived. You are still drinking, maybe. Or you stopped after we arrived.
In Romanian, the two tenses are called ”more than perfect” and respective ”imperfect”
I'm only taking this course for easy exp since Romanian is my native language. After hearing this sentence, no wonder there's a slower speed for the audio. The intonation at normal speed is weird af.