What makes the yardstick test a direct measurement of reaction time?

The yardstick test is considered a direct measurement of reaction time because the relationship between the distance the yardstick falls and the speed of a person's reaction is clearly defined. When a person is instructed to catch the falling yardstick, their reaction time can be measured by how far the yardstick drops before they catch it. Specifically, if the yardstick falls further before being caught, this indicates a slower reaction time, as a greater distance correlates to a longer time taken to respond. This straightforward relationship allows for an effective assessment of how quickly someone can react to a stimulus, making option A the correct choice in this context.

The other answer choices do have some merit but do not precisely address why the yardstick test specifically measures reaction time. For instance, while yardsticks do indeed have numerical markings, which can aid in measuring distance, this feature alone does not make the yardstick a direct measure of reaction time. The design of yardsticks for measuring length (as mentioned in another option) is not directly relevant to the testing of reaction time itself. Therefore, the core reason this test works effectively hinges on the correlation between the distance the yardstick falls and the individual's reaction speed, not solely on the yardstick's features or purposes.