"예쁜 여자가 수영하고 있어요."
Translation:The pretty woman is swimming.
I wasn't paying full attention and just wrote "The pretty lady is swimming", which is (apparently) not acceptable. I guess lady and woman have more significantly differing connotations than they do in English. If not, I vote that lady ought to be added as an alternative. Not really important, more just a suggestion. I saw the post from the course contributor and how much work goes into even small sentences with the many possibilities for alternative correct answers... It's insane.