Stimulus:

Clear markings on narrow road are expected to make driving safer particularly when visibility is poor.
When Greatwater County painted edges of narrow roads, the accident rate on those roads increased slightly.

This is what we call 'Explain the Paradox' question. You were expecting the accident rate to go down but it actually went up! We have to look for the option that will help explain this paradox.
1. That might explain why its accident rate is higher than that of other counties. It doesn't explain why its accident rate is higher than its own previous accident rate. It had the same narrow winding roads before, it has the same roads now.
2. In bad weather, it can be nearly as hard to see the road as at night. But the case was the same before the roads were painted. After the roads were painted, it should have been easier for the drivers to drive at night and also in bad weather. The accident rate should have dropped then. It doesn't explain why it increased after the roads were painted. (If the option had an additional statement saying 'There have been unusually high number of bad weather days recently (after the paint job)' or something like it, we might have given it more thought.
3. The comparison is not between accident rate of narrow roads and other roads but between the accident rate of narrow roads before the paint job and narrow roads after the paint job.
4. Again, doesn't explain the difference in accident rate before the paint job and after the paint job.
5. After the markings, drivers felt safer and drove on those roads at night too. If before the markings, let's say the accident rate was 2% and 100 people used to drive at night on those roads in a month, after the markings, the accident rate might have fallen to 1%, but 500 people started driving at night on those roads in a month. So there would be 5 accidents as compared to 2 of before. Therefore, we might have seen an increase in the accident rate. This explains the paradox.
(I just assumed the numbers I took above to give clarity)