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 from 34 to 40.
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 change. 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 the 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 the more important air pollutants, such as sulfur oxides, carbon monoxide, 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 a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased 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.
According to the passage, the numerical value of the concentration level of a substance is only useful if _____.
A. the other substances in the area are known
B. it is in a localized area
C. the natural level is also known
D. it can be calculated quickly
Giải bởi qa.haylamdo.com
C
Trong đoạn văn, con số về sự phân bố của một chất chỉ hữu ích nếu:
A. Các chất khác trong khu vực được biết đến
B. Nó đang ở trong một khu vực địa phương hóa
C. Mức độ tự nhiên cũng được cho biết
D. Nó có thể tính toán nhanh chóng
Dẫn chứng: “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.”
Tạm dịch: thực tế, giá trị về mặt số liệu cho chúng ta biết rất ít cho đến khi chúng ta biết những con số này biểu thị cho mức độ gia tăng lớn như thế nào dựa vào sự tập trung xảy ra tự nhiên trong khu vực.
Đáp án C
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
Mr.Brown has kindly agreed to spare us some of his _____ time to answer our questions.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
A survey was _____ to study the effects of smoking on young adults.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
Do you know the boy ______ at the party last week?
Mark the letter A, B, C, or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.
It is complicated because pollution is caused by things when benefit people.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
The exercises which we are doing ______ very difficult.
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
The girl packed the vase in polyester foam. She didn’t want it to get broken in the post.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
The United States consists of fifty states, ______ has its own government.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
The man ______ on the chair behind me kept talking during the film, ______ really annoyed me.
Mark the letter A, B, C, or D on your answer sheet to indicate the word(s) CLOSEST in meaning to the underlined word(s) in each of the following questions.
The government should do more to protect the environment.
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
He was suspected of stealing credit cards. The police have investigated him for days.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
Having finished her degree, ____.
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
A waitress served us. She was very impolite and impatient.
Mark the letter A, B, C, or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.
The man that you are looking for living next door.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
An endangered species is a species________ population is so small that it is in danger of extinction.
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
The _____________ friendly products are designed not to harm the natural environment.
