本句是called动词过去分词做后置定语，修饰a long chain of compounds. 后面是reactive(易反应的) components的定语从句

　　链接2 . （2017陕西卷）

　　Eating too much fatty food, exercising too little and smoking can raise your future risk of heart disease. But there is another factor that can cause your heart problems more immediately: the air you breathe.

　　Previous studies have linked high exposure(暴露) to environmental pollution to an increased risk of heart problems, but two analyses now show that poor air quality can lead to heart attack or stroke (中风) within as little as a few hours after exposure. In one review of the research, scientists found that people exposed to high levels of pollutants (污染)were up to 5% more likely to suffer a heart attack within days of exposure than those with lower exposure. A separate study of stroke patients showed that even air that the U. S. Environmental Protection Agency (EPA) considers to be of "moderate" (良好) quality and relatively safe for our health can raise the risk of stroke as much as 34% within 12 to 14 hours of exposure.

　　The authors of both studies stress that these risks are relatively small for healthy people and certainly modest compared with other risk factors such as smoking and high blood pressure. However, it is important to be aware of these dangers because everyone is exposed to air pollution regardless of lifestyle choices. So stricter regulation by the EPA of pollutants may not only improve environmental air quality but could also become necessary to protect public health.

【2017届高考英语二轮复习考点讲义：阅读理解-购物、饮食与健康】相关文章：

★ 2017届高考英语二轮复习书面表达限时测验：5（含解析）

★ 【人教版】2014届高考英语一轮复习指导考点针对练：必修1 unit4《Earthquakes》

★ 湖南省汝城二中2014届高考英语一轮复习阅读训练 (74)

★ 湖南省汝城二中2014届高考英语一轮复习阅读训练 (35)

★ 2017届高考英语二轮复习大题冲关秘籍完形填空之记叙文：命题趋势（含解析）

★ 【人教版】2014届高考英语一轮复习指导考点针对练：选修8 unit5《Meeting your ancestors》

★ 最新2016高考英语二轮复习的建议

★ 四川省2016届高考英语一轮复习课时作业（45） Module 3 Foreign Food 外研版选修8

★ 高考英语二轮复习策略2016

★ 【课堂新坐标】2017届高考英语（通用版）二轮复习短文改错专题训练：模式3 错一词（含解析）