With the question types:
- Drag & Drop
it is possible so select no correct answer and use it in a test (see picture match.jpg as example).
If the question is now answered correct (by not selecting any answer possibility) the Output Data delievers "FEEDBACKBASIC: empty" and no point (match1.jpg) although it would be correct.
Therefore it should be mandatory for these question types to have at least 1 right answer, like it is for multiple choice.