Which of the following can be inferred from paragraph 4 about Kramer s reason for filling one food box and leaving the rest empty? A. He believed the birds would eat food from only one box. B. He wanted to see whether the Sun alone controlled the birds' ability to navigate toward the box with food. C. He thought that if all the boxes contained food, this would distract the birds from following their migratory route. D. He needed to test whether the birds preferred having the food at any particular point of the compass.