I guess reporting would do in this case, as it is clearly a missing answer in Duo's dataset. Although it is less common to direct the question form of seeing in Progressive mode, it is a viable option.
I'm ok with it, because het (neuter) words in dutch tend to be the das (neuter) words in German so I can sort of fill in the gaps. Unfortunately, as with any language there are a gazillion exceptions to such rule so it doesn't always follow. It helps though.
i assume that you meant to say horse instead of house. If you did, then it's fine to say it like that, except that the dutch "Welk" translates as "Which", but in most cases "Which" and "What" are considered the same except in formal speech. (Pedants need not reply)