Usually the ascent of a mountain face is much easier than the . . . . . . .

The correct answer is C. descent.

The ascent of a mountain face is the act of climbing up the mountain, while the descent is the act of climbing down. The descent is usually more difficult than the ascent because it is easier to slip and fall when you are going down. Additionally, your muscles are tired from the ascent, so you may not have as much energy to use for the descent.

Option A, fall, is incorrect because it is not a type of mountain climbing. Option B, decent, is incorrect because it is a misspelling of the word “descent.” Option D, decent, is incorrect because it is an adjective that means “of good quality or standard.”