The climbers found the ascent nerve breaking.

Answer: Option D

Ascent : a climb or walk to the summit of a mountain or hill.
Slide : move smoothly along a surface while maintaining continuous contact with it.
Decline : (typically of something regarded as good) become smaller, fewer, or less; decrease.
Fall : move from a higher to a lower level, typically rapidly and without control.
Descent : an act of moving downwards, dropping, or falling.

Antonym of Ascent is Descent