For a hard inference question, determine what each piece of evidence supports and what limitation it introduces. Prefer the choice that preserves qualified conclusions—such as evidence being exaggerated rather than invalidated—and avoid choices that infer a specific cause or use when the passage establishes only that it is possible.
Hints
- Hint 1
Separate the evidence sources
Consider what the grain sizes, the chemical ratio, and the rainfall record each indicate independently.
- Hint 2
Distinguish amplification from fabrication
Ask whether charring creates the entire size difference or merely changes its apparent magnitude.
- Hint 3
Evaluate what a canal establishes
Use the stated alternative function of canals when interpreting the evidence from Site Q.
Step-by-step
- Step 1
Interpret the Site N evidence
The chemical ratio indicates that Site N’s barley received more water after the canal was built. Because the regional rainfall record shows no corresponding increase, irrigation is a plausible explanation for the added water.
- Step 2
Account for the effect of charring
The recreation shows that watering affects kernel size somewhat even before burning, so grain size is not useless evidence. However, charring shrinks water-stressed kernels more and therefore exaggerates the apparent size difference.
- Step 3
Use Site Q to limit the inference
At Site Q, canal construction is accompanied by neither chemical nor grain-size evidence of increased crop watering. Because canals could serve households instead of fields, the canal’s existence does not by itself establish irrigation.
- Step 4
Combine the findings
The evidence supports increased watering at Site N while qualifying the strength of the grain-size signal. It also cautions against inferring crop irrigation solely from the presence of a canal, which is why the fourth choice is best supported.