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 ...................

The author states that “There are no right or wrong answers” in order to ............

What use was made of the nineteenth-century women's history materials in the Schlesinger Library and the Sophia Smith Collection?

According to the passage, which of the following is TRUE about the 1987 supernova?

The phrase “For example,” line 19, introduces a sentence that gives examples of ........

The writer learnt to sail .................

The passage suggests that the first amphibians used their limbs to……..

The topic of this passage is______________.

What does the passage mainly discuss?

In order to show that learning to write requires effort, the author gives the example of ....................

This reading would most probably be assigned in which of the following courses?

Most of the public assistance programs ______ after the severe economic crisis.

How many Americans are involved in telecommuting?

It can be inferred from the passage that brain size is assumed to ___________.

Which of the following best expresses the main idea of the second paragraph of the passage?

According to the writer, why is the choice of your second job important?

Why are beta clockers not prescribed regularly?

What causes dodder to grow in a particular direction?

According to the passage, today’s Thanksgiving ..........

Which of the following statements is not TRUE about Thanksgiving ______?

According to the passage, which of the following is learning in broad view comprised of?