Understanding the Passage and Blank (6)

The passage discusses the Earth's changing climate, attributing some changes to natural causes and others to human activities like deforestation and industrial emissions. These activities lead to the accumulation of greenhouse gases in the atmosphere. The passage then explains the effect of these gases: they trap heat and _______(6) air temperatures near the ground. We need to find the most suitable word for blank (6) from the given options.

Analyzing the Sentence Structure for Blank (6)

The relevant part of the sentence is: "These gases are known as greenhouse gases because they trap heat and_______(6) air temperatures near the ground..."

The phrase "trap heat and _______ air temperatures" indicates that the word in the blank should describe the action that trapping heat performs on "air temperatures". Since "air temperatures" is the object of the action, we are looking for a transitive verb.

Evaluating the Options for Blank (6)

Let's examine the meaning and usage of each option:

• raise: This is a transitive verb meaning to lift or move something to a higher position or level, or to increase the amount, level, or strength of something. Example: "to raise prices", "to raise a hand", "to raise temperature".
• hike: This typically refers to walking a long distance for pleasure (intransitive) or, as a transitive verb, to increase something sharply, often prices or taxes. Example: "to hike up taxes", "to hike the price". While it means increase, it often implies a sharp or significant increase and isn't the most standard term for the gradual or general increase in average air temperature caused by trapped heat.
• rise: This is generally an intransitive verb meaning to move upward or to increase in amount or level. Example: "The sun will rise", "Temperatures are rising". You would say "air temperatures rise" but not "trap heat and rise air temperatures". It does not take a direct object like "air temperatures".
• balance: This means to make or keep something steady or in equilibrium. Trapping heat does the opposite of balancing temperature; it causes it to increase.

Determining the Best Fit

We need a transitive verb that describes how trapping heat affects air temperatures. Trapping heat causes air temperatures to go up or increase. The verb "raise" fits this perfectly as a transitive verb meaning to increase the level or amount of something, and it commonly used with temperature ("raise the temperature").

The structure "trap heat and [verb] air temperatures" requires a verb that acts upon "air temperatures". "Raise" does this, as in "they raise air temperatures". "Rise" does not fit grammatically here because it is intransitive; you would say "air temperatures rise" but not "they rise air temperatures". "Hike" is less appropriate in the context of a general description of the greenhouse effect on global air temperatures compared to "raise". "Balance" is completely contrary to the described effect.

Therefore, "raise" is the most appropriate word to fill blank (6).

Completing the Sentence

Substituting "raise" into the blank, the sentence reads:

"These gases are known as greenhouse gases because they trap heat and raise air temperatures near the ground..."

This sentence now accurately describes how greenhouse gases function.

Revision Table: Understanding Verb Usage

Additional Information: The Greenhouse Effect

The passage describes the basic mechanism of the greenhouse effect. Here's a little more detail:

• The Earth receives energy from the sun, mostly as visible light.
• The Earth's surface absorbs some of this energy and warms up.
• The warmed surface emits energy back towards space as infrared radiation (heat).
• Greenhouse gases (like carbon dioxide, methane, water vapor) in the atmosphere absorb this infrared radiation.
• Instead of the heat escaping to space, these gases re-emit the radiation in all directions, including back towards the Earth's surface.
• This trapped heat causes the Earth's lower atmosphere and surface to warm up, or raise the air temperature, much like the glass roof of a greenhouse traps heat, keeping the inside warmer than the outside.

Increased concentrations of greenhouse gases due to human activities enhance this effect, leading to global warming and climate change.