[单项选择]Landslides happen when large amounts of rock, mud and other loose materials are suddenly uprooted and sent sliding down a slope. This might be caused by an earthquake or it might happen after a heavy rain or when soil becomes waterlogged after a fall of snow.
As the material loses its grip and begins to move down the slope it gathers speed and sweeps up more material with devastating results. Nepal suffers from frequent landslides because the hillsides have been stripped of trees. When it rains the water soaks into the soil and this slides down the mountainside.
The worst landslide in Wales’ history came about with the collapse of an artificial mountain on 21 October 1966.
A 250-metre high mountain of waste material from the local coal mine had been piled up outside the village of Aberfan. Two million tons of rock, coal and mud began to move with a thunderous roar towards’the local school, uprooting trees and crushing houses. It was the start of the school day and
A. When large amounts of rock, mud and other loose materials are suddenly uprooted and sent sliding down a slope.
B. This might be caused by an earthquake or it might happen after a heavy rain or when soil becomes waterlogged after a fall of snow.
C. This might be caused by forest fire.
D. The hillsides have been stripped of trees which are rooted on them.