The answer is c because the precession of the ecliptic was component of a milankovitch cycle and is related to periodic ice ages through out history
The answer is Convergence of images behind the Retina
Convex lens converges light to a principal focus. The thickness of the lens determines the focal length (distance between the center of the lens and the principal focal point). Therefore, by evaluating the thickness of the convex lens, farsightedness, (an eye defect of convergence of images behind the retina) can be corrected by enabling images in the eye to form behind the retina.
