Most permafrost regions receive meager quantities of precipitation, amounts comparable to those of the world's deserts. Even so, soil is abundant.
Most of the permafrost, rock-hard even in summer, does not absorb moisture.
Consequently, what little precipitation does fall cannot penetrate the ground. Instead, it
on the surface. When the topmost layer of permafrost thaws in spring,
the moisture is held there, enabling vegetation to take root.

Fill in the blank:

A: dries
B: begins
C:collects
D:heats
E:Separates