Today I’d like to begin a discussion on the problem of the heating up the earth. First, we’ll touch on the relationship between fluorocarbons and the ozone layer. You probably remember that the ozone layer is the protective shield around the earth. It is important to all life, because it filters out harmful ultraviolet light from the sun. Ozone itself, a form of oxygen, is regularly made by the action of the sun in the upper atmosphere. It is also regularly destroyed by natural chemical processes.

The problem now is that too much of the ozone layer is being destroyed. Scientists suspect that certain chemicals, such as fluorocarbons, are contributing to the depletion of the ozone layer. And how do we use fluorocarbons? The most common uses are in spray cans and cooling systems. The chemical pollution from these fluorocarbons can account for some of the ozone losses that have been reported. There are, however, new studies linking the sun itself to the depletion of the ozone layer. We’ll go into that new study more next time.

The speaker’s main topic is ...................

Câu hỏi liên quan

• What can the word invokes be best replaced by?

• Which of the following statements does paragraph 1 support?

• The word "obscurity" could best be replaced by __________

ZUNIA12

• What does the word “which” in the fourth paragraph refer to?

• The word “triggering” is closest in meaning to __________

• The word “Ornaments” in paragraph 3 is closet in meaning to _______.

• According to paragraph 3, which of the following fields is NOT suitable for a person who does not want to live in a big city?

• The word “it” in paragraph 1 refers to ____________.

• According to the passage, red algae is ................

• What is the main idea of this passage?

• According to the passage, an exuberant tone of voice may be an indication of a person's ..............

• What can be inferred from the passage about supernovas?

• Which of the following is the author‟s main point?

• The word “retrieves” in paragraph 4 is closest in meaning to _______.

• What does the word "run" in the last paragraph mean?

• A housewife’s services in a family of five people are worth ............

• Around what time did the university begin to appear?

• Today, compared with 1910 ..............

• We can infer from the passage that ..............

• According to the first paragraph, how is the life changed since our parents time?