Looking beyond the 10-year period，the botanists estimate that some 3，000 native plant species may become extinct in the foreseeable future—more than 10 percent of the approximately 25，000 species of plants in the United States.
The situation is the same or worse in most other parts of the world.It is estimated that about 20 percent of Earth‘s approximately 300，000 plant species are in danger.Most of these plants are in the tropical rainforests that are being cut down，and many have not even been identified yet.
Why is extinction threatening so many U.S.species? The main reason is the destruction of habitats.This destruction is caused，especially in the Eastern United States，by land development，such as the construction of shopping centers and housing tracts.In the Western states，the poor management of public lands has been a critical factor.There，many habitats have been destroyed by the spread of exotic plant species.1)For example， June grass， which was introduced from Europe in the late 1800s， has invaded hundreds of square kilometers of Western lands，pushing out some native species of grass that are less able to compete for the usually scarce moisture.
Public indifference has also contributed to the problem.2) Americans have rallied to the cause of endangered animals such as whooping cranes and African elephants，but they seem unconcerned about endangered plants.Perhaps they consider wild animals to be public property，but plants are the property of the owner of the land on which they grow.
The consequences of habitat destruction are often most serious in the tropics and subtropics.Those regions have a much greater number of plant species than are found in cooler climates.And many species grow in only a small area，increasing the probability of their being wiped out.It is not surprising，therefore，that nearly 75 percent of the 680 species on the most-endangered list are located in just three states and Puerto Rico.Hawaii has 21 percent;Texas，12.2 percent;Florida，10.6 percent;and Puerto Rico，10.1 percent.But nearly all of the 50 states have at least a few native plants that are among those facing extinction.
Saving endangered plants is important for several reasons.Among those plants，there may be some that produce substances that could be of value in making medicines.Others might possess genetic traits that could be used to improve crop plants.We might also find that some plants are worth growing for their own sake—as food or perhaps for the oil in their seeds.But beyond such practical applications，there is a sense of loss when any species—a plant as much as an animal—disappears from the face of the Earth forever.
1. In another decade，it is estimated that____.
[A]more than 10 percent of the native plants in the United States may die out
[B]approximately 25，000 species of plants in the United States will be extinct
[C]20 percent of Earth‘s approximately 300，000 plant species will be extinct
[D]20 percent of Earth‘s approximately 300，000 plant species may become extinct
2. Which of the following is NOT mentioned as a cause of plant species extinction?
[A]Careless introduction of foreign plant species.
[B]Over-development of 1and for commercial use.
[C]Public ignorance of the present situation.
[D]Inappropriate governmental land protection policies.
3. In what way are the public indifferent to the present situation?
[A]They are still unaware of the cause of land destruction.
[B]They pay too much attention to endangered animals.
[C]They do not give due attention to saving endangered plants.
[D]They are selfish enough to protect only their own properties.
4. Plant species in the tropics and subtropics are most vulnerable in that____.
[A]a greater number of plant species are found there than in cooler regions
[B]many plant species grow in only a small area in these regions
[C]these regions frequently become the first targets of deforestation
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