Choose a, b or c as the best answer. 7. What is the purpose of the lecture?

Question

BlackTom AI · Accepted Answer

The lecture's main focus is the effects of water pollution on human health, which directly corresponds to option b.

1. Relevant knowledge points and concepts
- Listening for purpose: determine the speaker’s overall aim (general topic and intended message), not individual details.
- Distinguishing causes, effects, and safety guidance: “causes of shortage” (a) is about why scarcity occurs; “effects on human health” (b) is about consequences of pollution; “safety issues” (c) is advice on safe behavior. The correct purpose must match the overall emphasis of the lecture.

2. Step-by-step reasoning
- Step 1: Identify the general theme the speaker emphasizes throughout the lecture (what repeatedly appears, what the speaker explains or illustrates).
- Step 2: Compare that theme to each option: does the lecture explain reasons for water shortage (a), describe health consequences of polluted water (b), or give practical safety guidance about drinking polluted water (c)?
- Step 3: Choose the option whose scope matches the lecture’s primary content.

3. Intermediate steps / mapping to content
- If the speaker cites illnesses (cholera, dysentery), long-term effects (heavy-metal poisoning), statistics about disease burden, or mechanisms by which contaminants harm the body, these are explicit effects on human health → matches (b).
- If the speaker instead discussed factors like overuse, drought, infrastructure failure, that would support (a) — but those are absent in the lecture’s main thrust.
- If the talk mainly offered do’s and don’ts about how to avoid drinking polluted water (boiling, filtration), that would support (c) — again, that is narrower and procedural rather than explanatory.

4. Why the correct answer is correct
- Option b captures the broad explanatory aim: outlining the health consequences of pollution. The lecture’s examples, explanations of disease mechanisms, and emphasis on human health impacts demonstrate this purposive focus.

5. Why the other options are incorrect
- a. To outline causes of drinking water shortage — incorrect because the lecture deals with contamination effects, not the socioeconomic or environmental causes of shortages.
- c. To outline safety issues with drinking polluted water — incorrect because safety guidance is procedural and narrow; the lecture’s emphasis is on describing health effects rather than giving safety instructions.

6. Conclusion
Therefore, the best choice is b. To outline some effects of water pollution on human health. This matches the provided correct answer.

Choose a, b or c as the best answer. 7. What is the purpose of the lecture?单项选择题

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