Answer:
1000, 2000 and 3000.
Explanation:
The example given in the question is of a DNA with 4000 base pairs and it is being cut at 1000 pairs, 1500 pairs and 3000 pairs. So the lenghts of the segments that are cut from the original spiral are 1000, 500, 1500 and 1000 respectively. And the information that only the linear fragments are being produced is given to us in the question so the sizes of DNA expected would be 2000, 1000, 3000 and 2000 again respectively.
I hope this answer helps.