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C. only in the last fifty years.
D. for ages.
The unfavourable effects of cigarette smoking on the heart have frequently been described, but
the exact source for these effects has not been clarified. Some investigators believe nicotine to
be the culprit, and there has been some experimental work in animals indicating that large doses
of nicotine in conjunction with cholesterol feeding and vitamin D could produce a disease of
the arteries resembling that seen in humans. An alternative explanation has been offered by
other scientists who have pointed to the possible role of carbon monoxide being inhaled with
the cigarette smoke.
10. It is emphasized in the passage that nicotine ___.
A. is considered by some to be one of the reasons why smoking has
an adverse effect on the heart
B. is the only harmful factor in relation to smoking
C. affects animals more seriously than humans
D. has an adverse effect only upon the arteries
11. In accordance with the passage, studies into the adverse effects of smoking ___.
A. have ruled out any relationship between smoking and
cholesterol levels in humans
B. have not been able to establish for certain whether or not
carbon monoxide could be a factor
C. have so far not raised any controversial opinions
D. have shown that vitamin D reduces nicotine in the body
12. The main concern of the passage is to ___.
A. describe certain experiments on animals relating to the effects of carbon monoxide
B. emphasize the role nicotine and vitamin D play in heart
diseases
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