All three are accepted as translations. Klingon verbs are not marked for tense. In English we say "eat", "ate", "will eat", but in Klingon, you can't tell by looking at the verb, you have to look at the context to tell whether you are talking about something that happened in the past, will happen in the future, is happening right now, or happens on a regular basis. It's a little like the verb "to read". If I say, "I read the book," am I saying that it's something I do from time to time or am I saying that I have completed reading it? It can mean either, but context usually makes it clear: "Yesterday I read that book, but this is a book that I read every day." However, since very simple sentences lack that type of time context in Duolingo, you can't be sure how to translate the Klingon sentence. Thus, unless we have added something to the sentence that makes the time context clear, we accept translations in the past, the present, or the future.
An explanation of this is given in the Tips & Notes. It’s a lot of new information and some details are bound to slip through the memory. But since Duolingo has hidden the Tips & Notes I want to make sure you know about them and where to find them. If you have not been reading the Tips & Notes, I would like to ask that you review those so we don’t have to continuously repeat the information that we have explained there.
If you are doing the course on iOS or Android, you cannot currently access the Tips & Notes through the app. To access the Tips & Notes, you will have to access the course using a web browser at https://www.duolingo.com/. You can still do it on your mobile device, but you will have to use the web browser instead of the app (or you can do it from a computer). When you click on a Skill, it will expand to reveal a Start button, a key, and a light bulb.
If you click on the light bulb it will reveal the Tips & Notes and give you a detailed explanation of the grammar that is introduced in that Skill. If you have questions after reading the Tips & Notes for any Skills, then please return to the forum to ask your question, explaining what you didn’t understand or what seems contradictory to you.
Because of the fact that Klingon does move things around so much, we ask that you don't move things that don't need to be moved. While, there is usually no difference in meaning between "Mara and Torg" and "Torg and Mara", we ask you to treat them separately in this course. Mostly to stop learners from reading and writing sentences in reverse order. Learners need to learn that not everything changes order and so we are stricter than most languages would be on making learners maintain orders that do not need to be changed.