Part III Reading Comprehension (40 minutes)Directions: This part is to test your reading ability. There are 5 tasks for you to fulfill. You should read the reading materials carefully and do the tasks as you are instructedTasklDirections: After reading the following passage, you will find 5 questions or unfinished statements, numbered 36 to 40. For each question or statement there are 4 choices marked A), B), C) and D). You should make the correct choice and mark theccorresponding letter on the Answer Sheet with a single line through the center.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 microscope.Many 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 (PM 10) 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 size (about l/30th the average width of a human hair), fine particles can stay deeply into the lungs.Sources of fine particles include all kinds of burning activities such as motor vehicles, power plants, wood burning, etc. and certain industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse (粗的)".Sources of coarse particles include crushing or grinding operations, and dust from roads. Other particles may be formed in the air from the chemical change of gases. They are indirectly formed when gases from burning fuels react with sunlight and water vapor. These can result from fuel burning in motor vehicles, at power plants, and in other industrial processes.36. What does PM 2.5 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 greater health risks