17. _______ Which of the following is a theory, not a fact? (A) The Paleolithic period refers to a period of time that began about 2.6 million years ago. (B) Cordain is a nutritionist who studied the diets of hunter-gatherers who are alive today. (C) A diet similar to what people ate in the Stone Age can prevent many medical problems. (D) The Hadza people of Tanzania get almost 70 percent of their calories from plants.