So I put "large" and it says it must be "huge". if it can be "big", why not "large"?
Please report that during the lesson (the missing alternative and the incorrect alternative).
I don't think gross should be huge. I'd say it should be either large or big. "Huge" implies something unusual large/big which doesn't really make sense in that context. All in all, I think this should be changed because it confuses.
Yes, sure. Huge is riesig or something similar, but not just groß. Should be reported.