Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the answer to each of the
Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the answer to each of the questions.
Although only a small percentage of the electromagnetic radiation that is emitted by the Sun is ultraviolet (UV) radiation, the amount that is emitted would be enough to cause severe damage to most forms of life on Earth were it all to reach the surface of the Earth. Fortunately, all of the Sun’s ultraviolet radiation does not reach the Earth because of a layer of oxygen, called the ozone layer encircling the Earth in the stratosphere at an altitude of about 15 miles above the Earth. The ozone layer absorbs much of the Sun’s ultraviolet radiation and prevents it from reaching the Earth.
Ozone is a form of oxygen in which each molecule consists of three atoms (O3) instead of the two atoms (O2) usually found in an oxygen molecule. Ozone forms in the stratosphere in a process that is initiated by ultraviolet radiation from the Sun. UV radiation from the Sun splits oxygen molecules with two atoms into free oxygen atoms, and each of these unattached oxygen atoms then joins up with an oxygen molecule to form ozone. UV radiation is also capable of splitting up ozone molecules; thus, ozone is constantly forming, splitting, and reforming in the stratosphere. When UV radiation is absorbed during the process of ozone formation and reformation, it is unable to reach Earth and cause damage there.
Recently, however, the ozone layer over parts of the Earth has been diminishing. Chief among the culprits in the case of the disappearing ozone, those that are really responsible, are the chlorofluorocarbons (CFCs). CFCs meander up from Earth into the stratosphere, where they break down and release chlorine. The released chlorine reacts with ozone in the stratosphere to form chlorine monoxide (CIO) and oxygen (O2). The chlorine then becomes free to go through the cycle over and over again. One chlorine atom can, in fact, destroy hundreds of thousands of ozone molecules in this repetitious cycle, and the effects of this destructive process are now becoming evident.
Trả lời cho các câu 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 dưới đây:
Đáp án đúng là: B
Đáp án cần chọn là: B
Đáp án đúng là: D
Đáp án cần chọn là: D
Đáp án đúng là: C
Đáp án cần chọn là: C
Đáp án đúng là: B
Đáp án cần chọn là: B
Đáp án đúng là: C
Đáp án cần chọn là: C
Đáp án đúng là: C
Đáp án cần chọn là: C
Đáp án đúng là: A
Đáp án cần chọn là: A
Đáp án đúng là: A
Đáp án cần chọn là: A
Đáp án đúng là: B
Đáp án cần chọn là: B
Đáp án đúng là: A
Đáp án cần chọn là: A
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