单项选择题

In 1977 Irene Pepperberg did something very bold. At a time when animals still were considered automatic in behavior, she set out to find out what was on another creature’s mind by talking to it.
At that time, many scientists believed animals were incapable of any thought. They were simply machines, robots programmed to react to stimuli but lacking the ability to think or feel. "That’s why I started my studies with Alex," Pepperberg said. Alex was a one-year-old African gray parrot Pepperberg bought in a Chicago pet store. She let the store’s assistant pick him out because she didn’t want other scientists saying later that she’d intentionally chosen an especially smart bird for her work. Given that Alex’s brain was the size of a shelled walnut, most researchers thought Pepperberg’s interspecies communication study would fail.
Under Pepperberg’s patient instruction, Alex learned how to use his vocal tract to imitate almost one hundred English words. They were clearly a team-- and because of their work, the notion that animals can think is no longer so fanciful. Since Alex was able to produce a close approximation of the sounds of some English words, Pepperberg could ask him questions about a bird’s basic understanding of the world. Of course she couldn’t ask him what he was thinking about, but she could ask him about his knowledge of numbers, shapes, and colors. To demonstrate, Pepperberg took a green key and a small green cup from a basket on a shelf. She held up the two items to Alex’s eye.
"What’s same" she asked.
Without hesitation, Alex’s said. "Co-lor."
"What’s different" Pepperberg asked.
"Shape," Alex said. His voice had the digitized sound of a cartoon character. But the words--and what can only be called the thoughts--were entirely his.
And, then, as if to offer final proof of the mind inside his bird’s brain, Alex spoke up. "Talk clearly!" he commanded, when one of the younger birds Pepperberg was also teaching mispronounced the word green. "Talk clearly!" "They need to be able to distinguish colors to know when a fruit is ripe or unripe," Pepperberg noted. "They need to know the shapes of their enemies. And it helps to have a concept of numbers if you need to keep track of your flock. For a longlived bird, you can’t do all of this with instinct; cognition must be involved." The passage focuses on ______.