The correct answer should be A. environmental
Food variety is based on the location of the place. Before the discovery of the new world, nobody could eat corn or potatoes in Europe.
I believe the correct answer is: material that the lens is
made from.
Lenses are engineered to have
specific focal lengths, besides the curvature of the two sides of a lens. The
focal range, the distance between your optic nerve and the retins in lens, of
the lenses is determined by the material that lenses are made from.
