Why doesn't Duo Lingo teach the actual, complete alphabet. There should be a button where you can see the whole Greek alphabet, the name of each letter, and the phonetic pronunciation of the letter in sentences, like there is in every English-Greek dictionary, and like children would learn in school. We shouldn't be presented with letters that haven't been named and that we can't look up the name of and memorize, in the hope that seeing them in a word without any further explanation will accomplish this automatically. There is a very simple feature you could offer that would solve this problem. The same feature should be available for the Hebrew, Russian, Chinese and other alphabets with very different letters than those in English.
Ah, while I agree with you, Chinese doesn't have an alphabet
It's more of a mix of a logography and a syllabary. Because of this, nearly every word in Chinese has a separate character or group of characters. They don't use letters like we do. In English, each letter (roughly) represents a sound, but when you look at a word in Chinese, you won't inherently be able to say it. Altogether there are over 50,000 separate characters in written Chinese, so it would be a little impractical to have a full list :)