Choose a, b, c or d as the best answer.4. Which statement best summarises the main idea of this paragraph?

Question

BlackTom AI · Accepted Answer

The paragraph’s central claim is a policy prescription: carbon taxes should be used to reduce greenhouse gases.

1) Relevant knowledge points and concepts
- Main idea vs. supporting details: the main idea is the author’s overall point or recommendation; supporting sentences provide evidence or examples.
- Signal words for claims: modal verbs like “should” and policy language (e.g., “must,” “we should,” “policy,” “tax”) indicate a prescriptive main idea rather than a descriptive fact.
- Scope: a main idea must capture the paragraph’s primary focus, not a minor fact or background detail.

2) Step-by-step reasoning
- Identify the topic: all answer choices relate to climate change/greenhouse gases, so the paragraph is about global warming and its mitigation.
- Find the author’s stance: if the paragraph includes recommendation language or focuses on measures to reduce emissions, the main idea will be prescriptive (a policy recommendation).
- Compare scope and emphasis: option (b) is a clear action-oriented solution; options (a), (c), and (d) are descriptive statements about the problem or causes.

3) (No numeric calculations apply.)

4) Why the correct answer is correct
- Option (b) explicitly states a recommended solution—“Carbon taxes should be used to reduce greenhouse gases.” If the paragraph argues for using taxes as a tool and supports that claim with reasons or examples, this sentence captures the author’s central point and intent. The modal “should” signals a recommendation, which is exactly the typical main idea when a paragraph argues for policy change.

5) Why the other options are incorrect
- (a) “Global warming is an enormous and serious global problem.” This is a broad description; if the paragraph’s purpose is to advocate a specific policy, this is only background, not the main thrust.
- (c) “Carbon pollution is the main contributor to climate change.” This is a factual claim about cause, narrower than a policy recommendation.
- (d) “Climate change has impacted on global temperatures.” This is a specific factual detail, definitely not a policy prescription.

Conclusion: Given the paragraph’s emphasis on action and recommendation, option b is the best summary of the main idea. The final answer is: b. Carbon taxes should be used to reduce greenhouse gases.

Choose a, b, c or d as the best answer.4. Which statement best summarises the main idea of this paragraph?单项选择题

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