TOEFL iTP | Reading | Electromagnetic Raditation

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Although only a small percentage of 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, 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 chloroflurocarbons (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 (ClO) 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.

Longman
  1. According to the passage, ultraviolet radiation from the Sun
  1. Is causing severe damage to the Earth’s ozone layer
  2. Is only a fraction of the Sun’s electromagnetic radiation
  3. Creates electromagnetic radiation
  4. Always reaches the Earth
  • The word “encircling” in Line 5 is closest in meaning to
  1. Rotating
  2. Attacking
  3. Raising
  4. Surrounding
  • It is stated in the passage that the ozone layer
  1. Enables ultraviolet radiation to reach the Earth
  2. Reflects ultraviolet radiation
  3. Shields the earth from a lot of ultraviolet radiation
  4. Reaches down to the Earth
  • According to the passage, an ozone molecule
  1. Consists of three oxygen molecules
  2. Contains more oxygen atoms than the usual oxygen molecule does
  3. Consists of two oxygen atoms
  4. Contains the same number of atoms as the usual oxygen molecule
  • The word “free” in line 10 could best be replaced by
  1. Liberal
  2. Gratuitous
  3. Unconnected
  4. Emancipated
  • Ultraviolet radiation causes oxygen molecules to
  1. Rise to the stratosphere
  2. Burn up ozone molecules
  3. Split up and form as ozone
  4. Reduce the number of chloroflurocarbons
  • The pronoun “it” in line 13 refers to
  1. Radiation
  2. Process
  3. Formation
  4. Damage
  • The word “culprits” in line 16 closest in meaning to which of the following?
  1. Guilty parties
  2. Detectives
  3. Group members
  4. Leaders
  • According to the passage, what happens after a chlorine molecule reacts with an ozone molecule?
  1. The ozone breaks down into three oxygen atoms.
  2. Two different molecules are created
  3. The two molecules combine into one molecule.
  4. Three distinct molecules result
  1. Where in the passage does the author explain how much damage chlorine can do?
  1. Lines 1-3
  2. Lines 12-14
  3. Lines 18-19
  4. Lines 20-22
  1. The paragraph following the passage most likely discusses
  1. The negative results of the cycle of ozone destructions
  2. Where chloroflurocarbons (CFCs) come from
  3. The causes of the destruction of ozone molecules
  4. How electromagnetic radiation is created

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