9. Listen to the conversation again and answer the following questions:

1. Have Mary and Dr. Rowland met before? How do you know?

2. What is Mary interested in?

3. What have scientists theorized about for 30 years?

4. What does a doomsday scenario mean?

5. What is the scientists' argument?

6. When did the first Industrial Revolution take place?

7. What do geochemists worry about?

8. What will happen if the greenhouse scenario unfolds?

9. What is Dr. Rowland's forecast?

10. What are the measures to be undertaken at present to avoid negative effects of global warming?

10. Listen to the conversation once again and write out all the questions that Mary asks.

11. Ask your fellow students the questions you've written out and let them answer them. Do their answers agree with Dr. Rowland's replies?

12. Listen to the dialogue for the fourth time if necessary and say in what connection Mary interrupts the scientist and what she doesn't seem to understand.

13. Read the following text, divide it into logical parts and entitle them. Condense the sentences of the text where possible and write an abstract in your own words using your plan and the sentences that you've condensed.

MERCURY IN THE ENVIRONMENT

Mercury is known to be a rare metal. The element is found in trace amounts throughout the lithosphere (rocks and soil), the hydrosphere, the atmosphere and the biosphere (in tissues of plants and animals). In the rocks and soil mercury is found to be measured in fractions of one part per million. In the hydrosphere (the seas and fresh water) it occurs only in parts per million. In the atmosphere mercury is present both as vapour and in the form of particles. It should be noted, however, that under natural conditions the amount of mercury in the atmosphere is so small that extremely sensitive methods are required for detecting and measuring it. The situation is somewhat different in the biosphere. Plants and animals tend to concentrate mercury. For example, it has been found that some marine algae contain a concentration of mercury more than 100 times higher than that in the seawater in which they live. Mercury today is used on a substantial scale in chemical industries, it being used in the manufacture of paints and paper as well as in agriculture. The world production of mercury has been found to amount to about 10,000 tons per year. In agriculture mercury in the form of corrosive sublimates (HgCl₂) can be used for disinfecting seeds. The chlorides of mercury are employed in protecting a number of vegetable crops. Due to such large-scale uses a considerable amount of mercury wastes is likely to flow into the air, the soil, the streams, rivers, lakes. One might ask whether all these may present a threat to health? In order to answer this question it is necessary to examine the forms in which mercury occurs. Liquid mercury itself is not toxic to man, but mercury vapour, however, can be injurious. It has long been known that the soluble inorganic salts are toxic. So, knowing properties and forms of mercury, it is possible to use it. Mercury being very important, it is useful to continue investigating its properties very closely.

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