I wonder why #Duolingo writes stand-alone vowels with the initial ㅇ - if a word begins with a vowel then the vowel contains ㅇ, but I'd rather learn the vowels by themselves so I can identify them when they combine with consonants.
For example, a word-initial "e" is 에, but "e" in any other context is just ㅔ, and "ne" - "n" + "e" - is ㄴ + ㅔ = 네.
Duolingo just gives you 에, without any explanation that the ㅇ isn't actually part of the vowel form.