For some time now, medical scientists have noted an alarming increase in diseases of the heart
and circulation among people who smoke cigarettes. It has been 9 that the presence of
nicotine in the bloodstream causes blood vessels to contract, thus slowing circulation, a condition
which 10 leads to hardening of the arteries. As the arteries stiffen, 11 blood reaches the
brain, and the end result of this slowdown is a cerebral hemorrhage, commonly referred to 12
a stroke. 13 , nicotine in the bloodstream reduces the ability of the hemoglobin to release
oxygen, resulting in shortness of 14 , thus causing the person to breathe more rapidly. This
forces the heart to beat 15 —that is, the pulse rate increases—and in turn accelerates the risk
of a heart attack.
【題組】12. (A) is (B) for (C) as (D) in
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