Who among the following is most likely taking the traditional approach to the study of development?

The question is asking us to identify the person who is taking the traditional approach to the study of development. Option A emphasizes extensive change from birth to adolescence, little or no change in adulthood, and decline in old age, which is a traditional approach. Option B mentions Gregory, but it does not provide any information about his approach to the study of development. Option C mentions a multidisciplinary and contextual approach, which is not traditional. Option D emphasizes extensive change, but it does not provide any information about the other stages of development. Therefore, the correct answer is A, as it describes the traditional approach to the study of development.