"She lives in a house the roof of which is black."
Translation:Sie wohnt in einem Haus, dessen Dach schwarz ist.
Hmmm... "whose roof" sounds odd.
Aren't "whose", "who", and "whom" best with animate objects? Otherwise "that" works better? (Can anyone chime in on this grammerwise?)
E.g., "She lives in a house that has a black a black roof."
Even better would be: "She lives in a house with a black roof". But, then the point of the excercise is lost.
So for the point of this excercise (clauses), I like Duolingos translation best: "She lives in a house the roof of which is black."
I agree. The possessive relative pronoun in English is whose, regardless of the animacy of the possessor. The various phrasings which avoid any suggestion of animacy in the house are awkward. They have the air of the contortions people go to to avoid other false grammatical rules -- e.g., http://itre.cis.upenn.edu/~myl/languagelog/archives/001702.html .