Question 211·Hard·Rhetorical Synthesis
While researching a topic, a student has taken the following notes:
- Biochar is a charcoal-like material created by heating organic waste in the absence of oxygen (pyrolysis).
- When incorporated into soil, biochar improves water retention and nutrient availability.
- Biochar stores carbon that would otherwise re-enter the atmosphere and can remain stable for hundreds of years.
- Some studies show that biochar reduces nitrous oxide, a potent greenhouse gas, emitted from soil.
- The effectiveness of biochar varies with the type of feedstock used and the characteristics of the soil.
The student wants to draft a sentence explaining why many researchers consider biochar a promising tool for mitigating climate change. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions, identify the exact purpose (here, explaining why biochar is promising for climate mitigation), then select the option that is fully supported by the notes and most directly addresses that purpose. Prefer choices that combine multiple relevant notes, and eliminate choices that contain even small factual mismatches (process details, exaggerated certainty, or the wrong greenhouse gas).
Hints
Focus on the task words
Look for notes about carbon and greenhouse gases—those most directly support “mitigating climate change.”
Use multiple relevant notes
Prefer an option that combines more than one climate-related idea (for example, carbon storage plus reduced greenhouse gas emissions).
Check for subtle mismatches
Verify details like absence of oxygen during production and which greenhouse gas is mentioned in the notes.
Step-by-step Explanation
Restate the goal
The sentence must explain why researchers consider biochar promising for mitigating climate change, so it should use notes about carbon storage and/or reducing greenhouse gases, not just general soil improvement.
Pick the most relevant notes
The most directly relevant notes are:
- Biochar stores carbon that can remain stable for hundreds of years.
- Some studies show biochar reduces nitrous oxide, a potent greenhouse gas, from soil.
The production detail (heating organic waste without oxygen) can help define biochar accurately.
Eliminate choices that contradict or add unsupported details
- Any choice that says biochar is made with oxygen contradicts the note about heating organic waste in the absence of oxygen.
- Any choice that says stored carbon returns quickly contradicts the note that it can remain stable for hundreds of years.
- Any choice that claims biochar reduces a greenhouse gas not mentioned in the notes (like carbon dioxide from soil) is unsupported.
Select the choice that is accurate and directly supports the purpose
The best choice accurately describes how biochar is made (without oxygen) and explains climate benefits supported by the notes (long-term carbon storage and reduced nitrous oxide), directly linking these to climate-change mitigation.
Correct answer: Biochar, made by heating organic waste without oxygen, can store carbon for hundreds of years and may reduce nitrous oxide released from soil, so many researchers view it as a promising climate-change mitigation tool.