(WASHINGTON, Reuters)Research shows that two hours of exposure to elevated levels of car emissions raises the likelihood of a heart attack.
（路透社华盛顿电）研究显示，接触高浓度汽车排废气达两个小时时，会提高心脏病发作的可能性。

The risk of a heart attack increases 48 percent in the two hours after exposure and there is an increased risk even 24 hours after exposure.
接触废气两个小时之后，心脏病发作的危险性增加了4800，甚至经过廿四个小时之后也仍有增加心脏病发作的危险。
People should avoid going outside for a long period of time when air duality is poor.
空气质量差的时候，民众应该避免长时间外出。