While researching a topic, a student has compiled the following notes:
- The distance between Paris and Berlin is approximately 878 kilometers.
- Average carbon dioxide emissions per passenger-kilometer (pkm): short-haul commercial flight—245 g CO₂/pkm; high-speed electric train—41 g CO₂/pkm.
- Even when its electricity is generated from Germany’s relatively carbon-intensive grid, a high-speed train emits no more than 50 g CO₂/pkm.
- Aviation is responsible for about 3% of total global carbon emissions, and rail for less than 1%.
The student wants to refute the claim that traveling by high-speed train from Paris to Berlin releases more carbon dioxide per passenger than taking a flight on the same route, specifically by showing that the claim remains false even if the train’s electricity is generated from Germany’s relatively carbon-intensive grid. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For a rhetorical synthesis question with a qualified goal, identify every requirement in the goal before comparing the choices. Prefer the option that uses evidence tied directly to the specified condition, keeps quantities in comparable units, and draws only conclusions that the notes support; reject choices that are broadly accurate but omit the qualification, shift to aggregate evidence, or mishandle units.
Hints
Focus on the qualification
The goal includes a particular condition involving the source of the train’s electricity. Look for a choice that actually establishes its conclusion under that condition.
Distinguish two train figures
The notes provide both a general average for high-speed trains and a separate upper bound that applies under the carbon-intensive-grid condition. Decide which figure directly addresses the goal.
Compare like units
Look for a comparison in which train and flight emissions are expressed using the same per-passenger-kilometer unit.
Check how distance is used
A per-kilometer difference must be multiplied by the route distance before it can be described as the total difference for the trip.
Step-by-step Explanation
Identify the full rhetorical goal
The response must do more than compare typical train and flight emissions. It must show that the train still releases less CO₂ per passenger when its electricity comes from Germany’s relatively carbon-intensive grid.
Select the condition-specific evidence
The relevant rates are:
- High-speed train using electricity from Germany’s grid: no more than 50 g CO₂ per passenger-kilometer
- Short-haul flight: 245 g CO₂ per passenger-kilometer
The general train average of 41 g is less directly relevant because the goal specifically emphasizes the German-grid condition.
Account for the common distance
Both modes travel the same approximately 878 km. Multiplying both rates by that same distance preserves their ordering, so the mode with the lower per-passenger-kilometer rate also has the lower total emissions per passenger.
Choose the accurate synthesis
The first choice uses the grid-specific train limit, compares it with the flight rate in the same units, and correctly connects that comparison to the shared route distance. It therefore fulfills every part of the stated goal.