Look at the four squares,A,B,C , and D , which indicate where the following sentence could

be added to the passage. Where would the sentence best fit？

Thus, rockslides occur more frequently during the spring, when heavy rains and melting snow are most prevalent.

Many mass wasting processes are described as slides. Rockslides occur when a coherent mass of rock breaks loose and slides down a slope as a unit.A If the material involved is largely unconsolidated, it is called a debris slide. Slides are among the fastest and most destructive mass movements. Usually rockslides occur in a geologic setting where the rock layers are inclined, or where there are joints and fractures in the rock that are parallel to the slope.B When such a rock unit is undercut at the base of the slope, it loses support and the rock eventually collapses. Rain or snowmelt can trigger a rockslide by wetting the underlying surface to the point that friction can no longer hold the rock in place.C The fastest type of slide is a rock avalanche, in which a mass of rock literally floats on air as it moves downslope. The high speed of a rock avalanche is the result of air becoming trapped and compressed beneath the falling mass of debris, allowing it to move down the slope as a buoyant sheet. D