Translation:Hagelslag was the discovery of the previous century.
I always thought that 'ontdekking' had to do with things that already existed. Columbus did not invent America, he discovered it (again, because obviously the Native Americans beat him to it). So I guess the word 'uitvinding' would be more appropriate here. (Unless, of course, someone really discovered mouse droppings were edible
Exercises like this are so God-damned useless, in which the translation of some Dutch place or concept is simply the transliterated form of the Dutch word.
Also, as you approach the end of any course in Duolingo, there is always a noticeable falling-off in quality control of answers accepted.