"Spring is prettier than fall."
Translation:La primavera es más bella que el otoño.
"La primavera es más bonita que el otoño." is what I submitted, and it was not accepted as correct. In fact "bonita" was translated as "prettier" on Google Translate (which I know isn't always correct - though it is usually), and "bella" was translated as "more beautiful."
If you are sure your translation is otherwise correct, report it, using the button on the lower left, after you have answered the question. That will bring it to the attention of the course contributors, who, if they agree with you that your translation is correct, will add it to the list of alternative translations.