SORU: aşağıdaki parçaya göre cevaplayınız
It is clear from the passage that
Recent research in Canada suggests that our
arteries may narrow slightly when we breathe in
the sort of traffic pollutants found in urban areas
during rush hour. The small restriction in blood
flow may not be a problem for healthy people, but
it could be fatal for those with cardiovascular
disease. Researchers at the University of Toronto
asked healthy volunteers to inhale a mixture of
ozone and particles less than 2.5 micrometers
across for two hours. The width of their brachial
artery, a large vessel in the arm, reduced by
between 2 and 4%. Breathing ozone or
particulates by themselves, or breathing filtered
air, did not cause constriction. It is unclear how
this effect is mediated, but there can be no doubt
that heart disease and airborne pollution are
deadly allies. In the US, for example, the
Environmental Protection Agency has estimated
that air pollution contributed to 60,000 heartrelated
deaths in 1996. With the health stakes so
high, environmental scientists have been given
the task of measuring levels of different
particulates in the atmosphere, and tracking them
back to their source. A particle's behaviour is
partly determined by its density. But its size is the
most important factor, and the smaller particulates
are, the more potentially dangerous they are to
health.