For an inference question, identify each major finding and require the answer to accommodate all of them. Be cautious of choices that correctly reflect one finding but ignore another; here, a valid conclusion must address both the age-related plateau and the environmental difference between ravines.
Hints
- Hint 1
Separate younger and older surfaces
Consider whether lichen diameter changes equally across the entire 10-to-180-year range.
- Hint 2
Compare the ravines
Focus on what the different lichen sizes on same-aged surfaces reveal about environmental effects.
- Hint 3
Combine both findings
Look for a conclusion that recognizes both the method's useful range and the conditions under which comparisons are valid.
Step-by-step
- Step 1
Identify the age-related pattern
Within each ravine, lichen diameter increased with exposure age only through about 70 years. Because diameters varied little after that point, size could not reliably distinguish among the older surfaces.
- Step 2
Account for habitat conditions
Same-aged surfaces had different lichen sizes depending on whether the ravine was humid and shaded or dry and exposed. Therefore, a size measured in one habitat cannot be interpreted using observations from another habitat without additional evidence.
- Step 3
Choose the supported conclusion
The conclusion must reflect both limitations while preserving the method's usefulness for younger, environmentally comparable surfaces. Therefore, the correct answer is lichen size may help order the exposure ages of younger surfaces within comparable habitats, whereas older surfaces or surfaces from different habitats require evidence beyond size alone.