"Tú quieres un perro."
I translated this as "You would like a dog." The approved translations are "You want a dog" or "You want one dog", yet it marks my 'a' incorrect. Is it really the 'would like' that is incorrect? I am not sure what I did wrong.
Your sentence is tranlated as 'tú querrias un perro', it is conditional, this sentence is just a statement.