"Where is the bus?"
Do you mean "公交车"? Duo often "teaches" new words by just "slipping" them in as we progress; I try to have a dictionary app open as I go so I can look up anything new.
Sounds odd to me (a native speaker can verify?) but I think omitting 的 works: 哪里有公共汽车 but to me would emphasise WHERE over 公共汽车
More nonsense education designed for you to get things wrong without a chance. Stupid