Concern about extinction—the permanent loss of a species—motivates a wide variety of people to take action to protect animal species at risk of dying out. Animal protection and animal rights are familiar themes associated with the field of environmental activism. Certainly, endangered animals suffer no lack of support.
Surprisingly, some of the most endangered plants are species that, up until recently, were used by humans as necessary food crops.
In order to maximize productivity, farmers have chosen to focus on a handful of highyield crops that can be harvested efficiently. At one time, the number of plant species used by humans to meet their nutritional requirements numbered above 7，000. Now, it is around 150. Some experts even claim that humans actually rely on just twelve species of plants for most of their food.
A single food crop generally contains several species, which may be further divided into hundreds of varieties, but these varieties are quickly disappearing. Eighty percent of the corn varieties grown in Mexico in 1930 have disappeared.Ninety percent of the 10，000 wheat varieties cultivated in China 1949 are no longer used.
Crop diversity is a factor that ensures the continuation of certain beneficial natural processes in ecosystems—the cycling of nutrients, management of pests, and maintenance of water quality. Clearly, there is an urgent need to preserve the plant's irreplaceable crop diversity before it is lost completely.
A. You probably want to know the exact approach to protecting endangered plants.
B. Also, crop diversity provides the necessary gene pool to supply crops with a variety of traits(特点).
C. Threatened by current shortsighted farming techniques, crop diversity has shrunk dramatically.
D. However, endangered plants are defended by few.
E. Examples of losses in crop diversity have been recorded worldwide.
F. The permanent loss of plant species represents a huge threat to humanity.
G. Thanks to modern farming techniques, many countries have taken measures to protect them.
