"She eats an apple."
Translation:Hon äter ett äpple.
English "a" and "an" depend on whether the next sound is a vowel sound. But Swedish doesn't care about the sounds of vowels in English - so en and ett are based on the word's gender. Here's some extra info on that: https://forum.duolingo.com/comment/26420394/Answers-to-some-common-questions-on-grammar-that-beginners-have