Highway Departments Sometimes Drill Holes into Roadside Slopes Excavated into Regolith

Highway departments sometimes drill holes into roadside slopes excavated into regolith or weak rock.The holes are drilled to angle slightly upward from the curb,and after drilling is complete a perforated pipe is installed in each hole.How will this help stabilize the roadside slopes?

A) Air within the pipes will help dry out the slope.
B) Minerals will precipitate into the pipe where water enters it, making the slope stronger.
C) Air and bacteria that enter the hillside via the pipe will introduce rooting systems that will stabililize the slope.
D) Groundwater will flow into the pipes and drain out, thus decreasing the saturation of the slope.