Which among the following is the richest source of vitamin D?

The main natural source of vitamin D in the diet is in the livers of fish, which ingest ultraviolet-irradiated sterols (in phytoplankton and zooplankton) and store the vitamin D produced in their livers. A major source of vitamin D is its synthesis in the skin upon ultraviolet B (UV-B) (wavelength, 290-315 nm) exposure. Except for fish, food (unless foified) contains only limited amounts of vitamin D. Vitamin D2 (ergocalciferol) is obtained from plant sources and is the chemical form found in some supplements. Ref: Shoback D.M., Sellmeyer D.E. (2010). Chapter 17. Disorders of the Parathyroids & Calcium & Phosphorus Metabolism. In McPhee S.J., Hammer G.D. (Eds),Pathophysiology of Disease, 6e.