Irene Pepperberg Worked with an African Gray Parrot Named Alex

Irene Pepperberg worked with an African gray parrot named Alex. Her research revealed that:

A) Alex was capable of addition, subtraction, multiplication, and division problems, showing an innate understanding of numbers.
B) Alex was able to make requests and to answer simple questions about objects.
C) Alex's linguistic abilities were limited to the "parroting" of phrases that he heard Irene speak.
D) Alex showed no evidence of cognitive abilities, which isn't surprising given his brain was the size of a walnut.