"You do not have good beer."
Translation:Vy nemáte dobré pivo.
Well the way hints work is slightly complicated. The word HAVE can be in English used for they, we, you.... Anything but he-she-it. Duolingo collects all hints pertaining to a word, because in another sentence HAVE can mean nemají. It should offer the correct form on the top spot though.
The verb "mít" always takes the accusative.
- Mám mladého muže. - I have a young husband.
- Máš horkou kávu? - Do you have hot coffee?
We just can't see it in this exercise because in the neuter gender, the nominative form looks the same as the accusative ("dobré pivo").