This passage is about____________

Câu hỏi: Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer for each of the questions from 35 to 42.
DISAPPEARING SPECIES
Two hundred years ago, passenger pigeons were the most numerous birds in the worlD. A flock of passenger pigeons might include over two million birds. When they flew overhead, they darkened the sky for hundreds of miles. Today not a single one of these birds exists. Incredible as it may seem, all those millions of birds were hunted down for food, feathers, and sport.
The story of the passenger pigeon is just one of many sad stories about animals that have disappeared. At least, 461 species of birds and mammals have become extinct in the past 400 years. Many more species - about 555 mammals and 1,073 birds - are now at risk of extinct. Among reptiles, fish, and invertebrates, at least 2,961 are at risk. And among plant species the number at risk reaches 25,000.
The cause of this terrible destruction is always the same: humankind. Sometimes people have killed off species directly by hunting them, as with passenger pigeon. In other cases, people have caused extinction indirectly as with the dodo bird of Mauritius (an island in the Indian Ocean). Though brutally hunted by the first European settlers, some dodos managed to survive in the interior forests. However, these were soon eliminated by the cats, dogs, pigs, and rats the Europeans brought with them.
The most frequent cause of extinction, however, is the human destruction of the environment. On the Hawaiian Islands, for instance, European and American settlers cut down the forests for farmland. This killed off many of Hawaii's unique species of birds and plants. Even more dramatic, today, is the situation in the Amazon rain forest. Here, each square mile of the forest contains thousands of plant and animal species. These species depend on each other and on their special environment. When the trees are cut down, the environment changes or is destroyed altogether. And many species disappear forever.
Scientists are very concerned about the many species that are disappearing around the world. The loss of our fellow creatures is a loss for US as well. Not only do we lose the chance to learn more about ourselves and our environment. We also lose valuable economic or scientific resources. Many wild plants, such as the wild tomato and the wild sunflower, are useful in genetically improving food crops. Other plants or animals are useful in medical research. In this way, medicines have been found to help fight leukemia, cancer, and many other diseases.
Aside from the uses that research has already discovered, there may be countless more. Who knows what we are losing in the forests that are being cut down? Every year, as more plants and animals disappear, we lose opportunities for science and medicine. That means opportunities to improve our lives. The loss of species also means a narrower range of genetic possibilities in the world. Scientists do not know what that will mean, but they are worried.
This passage is about____________
A. many kinds of plants and animals.
B. how europeans destroyed species on mauritius.
C. how hunting causes animals to become extinct.
D. the extinctionof plants and animals.