Answer:
The correct answer is letter "A": Binocular disparity.
Explanation:
Binocular disparity refers to the slight difference in the caption of an image between the left and the right eye because of the eyes' horizontal separation -also known as parallax.
In the case, Akeelah extended an arm and then one finger of the same arm. After focusing on the finger, she closes and opens both her left and right eye. As a result, she perceives a little different between the sight of one eye and the other.