Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.
An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous changes. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled- a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.
Many of more important air pollutants, such as sulfur oxides, carbon monoxides and nitrogen oxides are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.
However, human production usually occurs in a localized area, such as a city. In such region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0. 08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however has a natural level of 0. 1 ppm and is not usually a pollutant until its level reaches about 15 ppm.
What does the passage mainly discuss?
A. How much harm air pollutants can cause.
B. The effects of compounds added to the atmosphere.
C. What constitutes an air pollutant?
Giải bởi Vietjack
Chọn đáp án C
- John: “Do you think that we should use public transportation to protect our environment?”
- Linda: “___________________”
Mark the letter A, B, C, or D to indicate the word whose underlined part differs from the three in pronunciation in each of the following questions.
Read the following passage and mark the letter A, B, C or D on your answer sheet to choose the word or phrase that best fits each other numbered blanks.
Wind is a clean source of renewable energy that produces no air or water pollution. And since the wind is free, operational costs are nearly zero (1) _______ a turbine is erected. Mass production and technology advances are making turbines cheaper, and (2) _______ governments offer tax incentives to spur wind-energy development. Drawbacks include complaints from (3) _______ that wind turbines are ugly and noisy. The slowly rotating blades can also kill birds and bats, but not nearly as many as cars, power lines, and high-rise buildings do. The wind is also variable: If it's not blowing, there's no electricity generated. Nevertheless, the wind energy industry is (4) _______. Thanks to global efforts to combat climate change, such as the Paris Agreement, renewable energy is seeing a boom in growth, in (5) _______ wind energy has led the way. From 2000 to 2015, cumulative wind capacity around the world increased from 17,000 megawatts to more than 430,000 megawatts. In 2015, China also surpassed the EU in the number of installed wind turbines and continues to lead installation efforts.
(Adapted from https://www.nationalgeographic.com/)
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best completes the following exchanges.
- Mike: “My first English test was not as good as I expected.”
- Thomas: “__________________”
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
I saw a terrible accident while I _________ on the beach.
The Japanese market _________ 35 per cent of the company's revenue.
The talks were meant to break down _________ between the two groups.
