Water Pollution
      The demand for freshwater rises continuously as the world’s population grows. From 1940 to 1990, withdrawal of fresh water from rivers, lakes, reservoirs, and other sources has increased fourfold. Of the water consumed each year, 69 percent is used for agriculture, 23 percent for industry, and 8 percent for domestic uses.
      Sewage, industrial wastes, and agricultural chemicals such as fertilizers and pesticides are the main causes of water pollution. In 1995, the US Environmental Protection Agency (EPA).  reported that about 37 percent of the country’s lakes and estuaries, and 36 percent of its rivers, are too polluted for basic uses such as fishing or swimming, during all or part of the year. In developing nations, over 95 percent of urban sewage is discharged untreated into rivers and bays, creating a major human health hazard.
      Water runoff carries fertilizing chemicals such as phosphates and nitrates from agricultural fields and yards into lakes, streams, and rivers. These combine with the phosphates and nitrates from sewage to speed the growth of algae, a type of aquatic plant. The water body may then become choked with decaying algae, which severely depletes the oxygen supply. This process can cause the death of fish and other aquatic life. Runoff also carries toxic pesticides and urban and industrial wastes into lakes and streams.
      Erosion, the wearing away of topsoil by wind and rain, also contributes to water pollution.  Soil and silt washed from logged hillsides, plowed fields, or construction sites, can clog waterways and kill aquatic vegetation. Even small amounts of silt can eliminate desirable fish species. For example, when logging removes the protective plant cover from hillsides, rain may wash soil and silt into streams, covering the gravel beds that trout or salmon use for spawning.
      The marine fisheries supported by ocean ecosystems are an essential source of protein, particularly for people in developing countries; approximately 950 million people worldwide consume fish as their primary source of protein. Yet pollution in coastal bays, estuaries, and wetlands threatens fish stocks already depleted by over fishing. In 1989, 260, 000 barrels of oil was spilled from the oil tanker Exxon Valdez into Alaska’s Prince William Sound, a pristine and rich fishing ground. In 1992 there were 8, 790 reported spills in and around U. S. waters, involving 5. 7 million liters (1. 5 million gallons) of oil.

1. According to this passage, which of the following statements is true of yearly water consumption?
  A. Most water is used for home cooking.
  B. Most water is used for farming.
  C. Cities use more water than rural areas.
  D. America uses 8 percent of the world water resources.

2. Paragraph 2 suggests all of the following EXCEPT that
  A. fish may die because rivers may contain industrial wastes.
  B. it may be dangerous to swim in a river because the water may contain pesticides.
  C. EPA is responsible for causing serious water pollution in America.
  D. water pollution is rather serious in America.

3. Water runoff causes fish to die partly because
  A. they are rushed into agricultural fields and yards.
  B. they are choked by the water body.
  C. the poisonous algae have killed them.
  D. the fast-growing algae have used up the oxygen in the water where they live.

4. An important idea of paragraph 4 is that
  A. cutting down too many trees may also cause water pollution.
  B. erosion is caused by wind and rain alone.
  C. there are no longer desirable fish in the world.
  D. trout and salmon usually spawn in silt.

5. The main subject of the last paragraph is
  A. Fish as a Source of Protein. 
  B. The Increasing World Oil Production.
  C. Oil Spills and Pollution of the Sea.
  D. A World-famous Oil Tanker.
DNA Fingerprinting
      DNA is the genetic material found within the cell nuclei of all living things. In mammals the strands of DNA are grouped into structures called chromosomes. With the exception of identical siblings (as in identical twins), the complete DNA of each individual is unique.
      DNA fingerprinting is sometimes called DNA typing. It is a method of identification that compares bits of DN A. A DAN fingerprint is constructed by first drawing out a DNA sample from body tissue or fluid such as hair, blood, or saliva. The sample is then segmented using enzymes, and the segments are arranged by size. The segments are marked with probes and exposed on X-ray film, where they form a pattern of black bars—the DNA fingerprint. If the DNA fingerprints produced from two different samples match, the two samples probably came from the same person.
      DNA fingerprinting was first developed as an identification technique in 1985. Originally used to detect the presence of genetic diseases, it soon came to be used in criminal investigations and legal affairs. The first criminal conviction based on DNA evidence in the United States occurred in 1988. In criminal investigations, DNA fingerprints derived from evidence collected at the crime scene are compared to the DNA fingerprints of suspects. Generally, courts have accepted the reliability of DNA testing and admitted DNA test results into evidence. However, DNA fingerprinting is controversial in a number of areas: the accuracy of the results, the cost of testing, and the possible misuse of the technique.
      The accuracy of DNA fingerprinting has been challenged for several reasons. First, because DNA segments rather than complete DNA strands are “fingerprinted”; a DNA fingerprint may not be unique; large-scale research to confirm the uniqueness of DNA fingerprinting test results has not been conducted. In addition, DNA fingerprinting is often done in private laboratories that may not follow uniform testing standards and quality controls. Also, since human beings must interpret the test, human error could lead to false results.
      DNA fingerprinting is expensive. Suspects who are unable to provide their own DNA to experts may not be able to successfully defend themselves against charges based on DNA evidence.
      Widespread use of DNA testing for identification purposes may lead to the establishment of a DNA fingerprint database.

1. According to the essay, we can find chromosomes
  A. in a fish.      B. in a tree.        C. in a sheep.      D. in a rock.

2. DNA fingerprinting is more often used for
  A. obtaining samples of chromosomes.
  B. providing evidence in court investigations.
  C. proving the horse to be a mammal.
  D. printing books about biology.

3. When your brother looks exactly like you, your complete DNA may be
  A. exactly like his.                        B. totally different from his.
  C. unique.                                    D. lost.

4. Some people believe that using a DNA fingerprint may not be so reliable because
  A. the accuracy of DNA fingerprinting has been challenged.
  B. no private laboratory follows uniform testing standards or quality controls.
  C. mistakes are possible when researchers explain what have come of their tests.
  D. suspects may not have enough money to provide their own DNA to law-courts.

5. This essay talks about DNA fingerprinting concerning the following aspects EXCEPT
  A. legal application of the method.
  B. the way to obtain a DNA sample.
  C. work yet to be done about DNA fingerprinting.
  D. possible danger in drawing a DNA sample from the human body.