"She takes off a ring."
Translation:그녀가 반지를 빼.
In Korean there are many ways to way "to wear" and "to take off," depending on what the item is. If you get a Korean textbook, there will be a chapter on wearing things. Hat, glasses 쓰다. clothes 입다. ring, gloves 끼다. belt 차다. shoes, socks 신다. etc. Many of those words also have corresponding ways of saying "take off." You have to memorize them.
그녀는 반지를 빼요: Completely incorrect, apparently. Duo... seriously? There is absolutely nothing worse or frustrating than using a language program that absolutely will not accept any answer that is not exactly the one they had in mind. It also is counting the 가vs는 wrong, when there's only one subject in the sentence! My god... really?!
@duolingo: here suddenly you accept 그녀가 반지를 빼요 Would be appreciated that you give the grammatical/logical reason why here the ~요 is accepted, and not here: 우리는 반지들을 빼지 않아 . just as an exempel, there are many other phrases when sometimes it is accepted, sometimes not: I do not get the grammatical rule.