The correct answer is D. Selective attention.
The Stroop test measures the ability to selectively attend to the relevant aspect of a stimulus while ignoring other aspects that are irrelevant or distracting. In this task, the word "blue" is presented in a color that is incongruent with the meaning of the word (e.g., the word "blue" presented in red letters). This requires the participant to inhibit their automatic response to read the word and instead focus on the color of the word. Selective attention is a cognitive function that allows individuals to filter out irrelevant or distracting information and focus on the relevant aspects of a task. Research has shown that older adults have more difficulty with selective attention tasks compared to younger adults, which can impact their ability to perform everyday activities that require this cognitive function.