【答案解析】Because of the decline of water resources caused by global warming, it is still difficult to curb (check)desertification. The desert in the west of China is enlarging(spreading)at the(an annual) rate (speed) of 310 square kilometers a year. That is to say, China loses land the size of a medium- sized county. When cattle eat all the vegetations in sight (they can see), the top soil will be blown away, leaving nothing but sand behind / nothing but sand remains. Frequent sandstorms send us a warning that to destroy nature is to head for (seek / invite) self-destruction.