I replied: "The streets are beautiful"; which was graded wrong. The correct answer was: "The streets are pretty."
"Pretty" and "Beautiful" are a synonym, so both should be correct.
Why is the answer "These streets are pretty" not accepted? It is more of a demonstrative pronoun than an article.
I used "road" instead of "street" ("The roads are pretty") Is that really wrong? I could imagine a distinction like улица vs. дорога in Russian.