What is the meaning of the following traffic sign?

1. Steep escent for the next 2,500 meters.
2. Steep escent starts in 2,500 meters.
3. Correct answer: Steep and winding descent for the next 2,500 meters.
4. Steep descent starts in 2,500 meters.

WhyA '2,500 m' plate under a descent sign means the steep descent starts here and lasts 2,500 meters. If the descent only began after 2,500 m, the plate would be different.