9 out of 10, got the Luger one "wrong", but I regard it as a trick question.
It was originally chambered in 7.65mm Luger, as any autoloader aficionado knows
, so the caliber upgrade to 9x19 hardly counts as an "innovation"
in the context presented. Seen in that light, I suppose you could argue that 5.56x45 round was the most innovative part about the M16, not the direct gas-impingement operating system first seen on its direct predecessor, the .308-chambered AR10. I guess the "famously associated with Nazi officers" part was the clue, as that would rule out 7.65mm-caliber Luger pistols.
I got the DPM/Bren/MG42/Browning one right, but I agree that it's somewhat misleading to describe the MG42's descendents as "MG42s", if only because of the caliber changes, etc. As we've seen, apparently a change in caliber constitutes a major "innovation", according to the authors of the quiz.
Good link though, thanks!