The conclusion of a Holmes t' analysis suggesting clear distinguishability between two pendulum samples implies a significant difference. Option c) "Their t' was larger than 3" is a plausible inference.
The conclusion drawn from the Holmes t' analysis is that the two samples (pendulums with different masses) are clearly distinguishable. Let's evaluate the given answer choices in light of this conclusion:
1. **The period of a pendulum doesn't depend on mass.**
- This option contradicts the conclusion, as the analysis suggests that the periods are distinguishable, indicating some dependence on mass.
2. **The two masses might have been too similar.**
- This option contradicts the conclusion as well. The conclusion is that the masses are clearly distinguishable, suggesting that they are not too similar.
3. **Their t' was larger than 3.**
- This option is a possibility. A t' value larger than 3 suggests a significant difference between the two groups. However, the specific t' value is not mentioned, so we cannot confirm this option without the actual value.
4. **They found a limitation of the equation t.**
- This option is vague and does not directly address the conclusion. It doesn't provide information on whether the periods are distinguishable or not.
Given the information provided, option 3 is a possible inference, but the certainty depends on the actual t' value and the significance level chosen for the analysis.