阅读短文，从每题所给的A、B、C和D四个选项中，选出最佳选项。
In 1845, a deadly disease struck the farms of Ireland, killing all the
Lumper potato plants. In another place or time, the death of single crop
species (物种)
might not have been so important. But in Ireland, in 1845, people depended
almost solely on the potato for food. The death of one species caused a
terrible famine(饥荒). Now, some scientists are worried
that such a famine could happen again, but on a much wider scale.
Over the centuries, farmers have discovered thousands of different
species of food crops. Each species has special qualities. Some can be grown in
very hot or cold climates. Others are not affected by certain diseases.
However, you won't find many of these species in your local supermarket. To
feed the seven billion people on Earth, most farmers today are growing only
species of plants and farming only species of animals that are easy to produce
in large numbers.
For example, in the Philippines, there were once thousands of varieties
of rice: now fewer than 100 are grown there. In China, 90 percent of the wheat
varieties grown just a century ago have disappeared. Scientists believe that over
the past century, we have allowed more than half of the world's food varieties
to disappear.
One solution to this problem is to collect and store the seeds (种子) as many different
plant varieties as we can before they disappear. The idea was first suggested
by Russian scientist Nikolay Vavilov. In the 1920s and 1930s, he collected
around 400,000 seeds from five contients. More recently, others are continuing
the work he began.
In the U.S. state of Iowa, Diane Ott Whealy wanted to protect historic plant varieties, like the seeds her great –grandfather brought to the U.S. from Germany more than a hundred years ago. She and her husband started a place called Heritage Farm, where people can store and trade seeds.
More importantly, the people at Heritage Farm don't just store the seeds; they plant them. By doing this, they are reintroducing foods into the marketplace that haven't been grown for years. These food species are not just special in terms of appearance or taste. They also offer farmers food solutions for the future, from the past.
