So the only answer that's false in any case is 1500m. The others may all be correct, depending on the altitude: 3km below 3000 feet, 5km between 3000 feet and FL100, and 8km above FL100.
Now I'm confused....... So which is the correct answer that "they" were looking for if the other 3 answers are true?
I'm assuming the answer is 3km if as the question states there are '... no additional qualifications'?