Topsoil erosion is such a large problem because .
topsoil is found in such small quantities on the Earth’s surface
topsoil takes a long time to replenish
the developed world depends on crops grown in topsoil
the developing world depends on crops grown in topsoil
it exacerbates climate change and global warming
The practice of "slash and burn" is widely considered to be .
a relatively new invention
not sustainable
typical for tropical forests
found in high mountainous regions
