题目
you must choose the best answer from the four choices marked A, B, C and D.Choose the best one and mark your answer on the ANSWER SHEET with a single bar through the center of the letter that indicates your choice.2.1 Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, smoke, and liquid droplets.Particles can stay in the air for long periods of time Some particles are large or dark enough to be seen as smoke Others are so small that they can only be detected with an electron microscopeMany manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM.These solid and liquid particles come in a wide range of sizes.Particles less than 10 micrometers in diameter (PM10) cause a health concern because they can go into and accumulate in the respiratory system (呼吸系统).Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as "fine" particles and are believed to pose the greatest health risks.Because of their small size2.1.1 What does PM2.5 refer to?A Particulate matter found in the air.B.Dust, dirt, smoke and liquid droplets around us.C.Particles smaller than 2.5 micrometers in diameter.D.Particles which are believed to cause the greatest health risks.
you must choose the best answer from the four choices marked A, B, C and D.Choose the best one and mark your answer on the ANSWER SHEET with a single bar through the center of the letter that indicates your choice.2.1 Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, smoke, and liquid droplets.Particles can stay in the air for long periods of time Some particles are large or dark enough to be seen as smoke Others are so small that they can only be detected with an electron microscopeMany manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM.These solid and liquid particles come in a wide range of sizes.Particles less than 10 micrometers in diameter (PM10) cause a health concern because they can go into and accumulate in the respiratory system (呼吸系统).Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as "fine" particles and are believed to pose the greatest health risks.Because of their small size2.1.1 What does PM2.5 refer to?A Particulate matter found in the air.B.Dust, dirt, smoke and liquid droplets around us.C.Particles smaller than 2.5 micrometers in diameter.D.Particles which are believed to cause the greatest health risks.
题目解答
答案
C
解析
本题考查对文章中PM2.5定义的理解。关键在于识别文章中对PM2.5的直接描述。文章明确指出PM2.5是直径小于2.5微米的颗粒物，需注意区分PM2.5与其他颗粒物（如PM10）的定义差异，以及避免混淆颗粒物的健康风险与物理定义。
关键信息定位
文章中明确说明：
Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as "fine" particles...
选项分析
- A选项（Particulate matter found in the air）是PM的总称，而非PM2.5的特定定义。
- B选项（Dust, dirt, smoke and liquid droplets around us）描述的是PM的组成部分，未涉及PM2.5的尺寸标准。
- C选项（Particles smaller than 2.5 micrometers in diameter）直接对应文章中PM2.5的定义。
- D选项（Particles which are believed to cause the greatest health risks）描述的是PM2.5的健康风险，属于其特性而非定义。