Why does the author of "The Think Tank" include the detail that some scientists at the National Zoo's Think Tank focus on how animals use tools? A. to show that the ability to master language demands higher level thinking than using tools demands B. to show that Shumaker is one of the most advanced researchers at the National Zoo C. to show other ways that people are trying to learn about how animals think D. to show the types of studies that Shumaker considers to be most valuable