"Marcus is a man."
Translation:Marcus est vir.
Although word order in Latin is relatively free, the preferred/default is SOV. So it certainly ought to accept "Marcus vir est" and if it doesn't, please flag it and report "My answer should be accepted" so that the course contributors can fix it.
Sum is 1st person singular (Ego sum - I am), est is 3rd person singular (Is est/Ea est - He/She is).
Taking a latin course in university a few years ago, I was led to believe that the "est" can be dropped/assumed in sentences like this. Could a reasonable case be made that "Marcus vir" is an acceptable translation?
I don't believe so (after checking with Latin experts) but if you happen to have a source for that I'd be interested.
I know it's early and this is beta, but scanning the course I note that none of the cases are mentioned. I'm just glad you added Latin as I've always had a great interest in it. Will you eventually be adding cases, like the Dative, Accusative, etc." I honestly would like to know--and thanks again for the course. I've waited a long time for it. (As you can note! ;) )