The correct answer is option A, that is, snowline.
Explanation:
The climatic boundary between a snow-covered and snow-free surface is known as a snowline. The real snowline may amend seasonally, and be either substantially lower or higher in elevation. The permanent snowline refers to the level, that is, above which all the year snow will lie.
It is an umbrella term for various elucidations of the boundary between the snow-free surface and snow-covered surface.
