16. The focal length of a thin convex lens (凸透鏡) is f_air in air, or f_water in water. Which statement is correct?
(A) The focal length of a lens is determined by the surface curvatures only, so f_air is equal to f_water.
(B) f_air is smaller than f_water.
(C) It will be possible that a concave lens (凹透鏡) in water becomes a convex lens.
(D) Both f_air and f_water are independent on the frequency of incident light.
(E) None in above.