For many years the earth has been unable to provide enough food for these rapidly expanding populations, and the situation is steadily getting worse since the fertility of some of our richest ____ has been lost and vast areas that were once fertile lands have turned into____. And the trouble with deserts is that they____ to spread outwards on to the fertile soils. What is now the northern Sahara Desert    much of the civilized world 2,500 years ago.
Even at this moment, many of the earth’s natural treasures are being_____, many valuable animals and plants are being killed off , and it is becoming ____difficult to grow enough food to prevent much of the earth's population from____. The situation is getting out of hand. Time is running out. ____, with your help, we may be able to reverse(逆转) the trends which____our very existence.

A．treasure B．soils C．countries D．farms

A．factories B．cities C．deserts D．forests

A．pretend B．like C．prefer D．tend

A．brought B．lived C．fed D．grew

A．lost B．protected C．increased D．destroyed

A．increasingly B．rapidly C．properly D．perfectly

A．starvation B．poverty C．suffering D．disease

A．Besides B．Moreover C．However D．Therefore

A．protect B．threaten C．benefit D．rebuild