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.
so why did you reject "the streets are attractive" and "the streets are nice" as acceptable answers?
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.
ulice is really a street (except some English streets have "road" in their name) and a road is silnice, cesta