"He is in between."
Translation:Hij zit ertussen.
context! The comment posted by dwarven_hydra is a good help. However I must add to that: the verb 'zijn' can also be used for position. for example: 'De jongen is in de badkamer' (we don't know if is he is standing upright to brush his theeth, sitting on the toilet, or maybe lying in the badtub. But when asked: where is the boy? we do know that he is in the bathroom. so we say ' hij is in de badkamer'. Would he be in his own room we use 'zitten' again because thats the most probable position. (unless context gives us the boy is ill or something)
In this particular sentence however something else needs to be explained. 'Ertussen zitten' is a word combination frequently used for something else. I'll give you some examples to explain it. If you are looking at a lot of stuff at lost luggage but you don't see your bag, you can say ' hij zit er niet tussen'. So 'ertussen zitten' can refer to something that is amongst other stuf. In a identification line up the policeman would ask you ' zit hij ertussen?' (even though the men are standing). When I read the sentence for the first time I immediately thought of this meaning (you were searching for something or someone and found it). But for al we know it is about a thumb stuck in between the door. there is no context given whatsoever so we simply can't tell.
This comment became sort of an extra lesson, but I hope it helps anyway. Good luck! (by the way I'm a Dutch native speaker and was placed only at Dutch-level 10 by duolingo all because of multi-interpretable stuff like this, so don't give when duolingo tells you you are wrong!)
Even though The Netherlands are a relatively small country, there are lots of dialects! Many Dutch people are at a loss when they hear a dialect from a different area, especially when there is some considerable distance between the regions. In news items on tv, subtitles are used when Dutch dialect speakers appear. What you're learning here is standaardnederlands, our common standard language.