Read the excerpt from "The Think Tank". Shumaker is delighted with Azy's mistake. "Azy's mistakes are more interesting than his right answers," he says. "When he saw the bags, he didn't pick a symbol that meant food, such as 'apple.' He didn't pick a verb, such as 'open.' He picked the one other symbol that meant an object, a container. I think his mistakes show that he's putting these words into categories in his mind. Maybe this can teach us a little bit about how he thinks."
Which statement best explains how the passage supports the author's purpose?

The purpose is to criticize; the author believes that the orangutan experiment has no credibility.
The purpose is to instruct; the author wants readers to know they themselves can train orangutans to understand language.
The purpose is to inform; the author is bringing readers' attention to Azy's humanlike behavior.
The purpose is to persuade; the author is proving that Azy is the smartest orangutan in captivity.