阅读下面材料，在空白处填入适合的内容（一个单词）或括号内单词的正确形式。
Nowadays, many cities are suffering from smog, the short form of smoke and fog. It is especially harmful to children, seniors, pregnant women, smokers and people 61 lung or heart problems.
An important component (成分) of smog is ground-level ozone (地面臭氧). Actually, ozone that is formed naturally in the atmosphere 62 (protect) life from the sun’s damaging rays. At ground level, however, ozone hurts people’s eyes, nose, and throat, which can make 63 more difficult for the body to fight against an 64 (infect). When the amount of ground-level ozone increases, so does 65 number of emergency-room visits.
The other component is fine particulate matter (细颗粒物). The 66 (small) the particle (particulate matter 2.5, PM2.5), the more dangerous it can be. When people take in ozone and particulates from the air, both the blood flow 67 the oxygen supply to the heart will be reduced. [来源:学*科*网Z*X*X*K]
With such unhealthy air quality, some simple ways are recommended for you 68 (reduce) higher risk of health problems. On smoggy days, spend less time outdoors. If you have to get outside, close all your windows 69 you go out. Besides, roll up the windows of 70 car if you are driving.
【答案】
61. with
62. protects
63. it
64. Infection
65. the
66. smaller
67. and
68. to reduce
69. before
70. your
【解析】
试题分析:本文讲述了臭氧和空气中的颗粒物对人们身体的影响。
61. with 本句使用介词短语with lung or heart problems修饰名词people，指患有肺部或者心脏问题的人。
62. protects 本句中that is formed naturally in the atmosphere是定语从句，修饰先行词ozone，所要填的protects在句中做谓语动词。
63. it 句中的it是形式宾语，真正的宾语是后面的不定式短语。
64. Infection 介词against后面要接名词作宾语，infect是动词，其名词形式为infection。
65. the 本句中的the number of与前面一句中的the amount of…形成呼应关系。
66. smaller 本句是一个固定句式：the+比较级，the+比较级；表示“越…就越…”
67. and 固定搭配both…and…当人们吸入空气中的臭氧和颗粒物的时候，血液流动和心脏的氧气供应都会减少。
68. to reduce 本句考查不定式的复合结构for sb to do sth，一些简单的方法被推荐让你来减少心脏病的危险。
69. before 句意：在你外出之前，关闭所有的窗户。本句中的before引导起时间状语从句。
70. your 本句考查上下文串联。句意：如果你在开车，请把车子的窗帘卷起来。