Final answer:
Vitamin B-12 is mainly acquired through the consumption of animal products such as meat, fish, dairy, and eggs, as it is produced by bacteria and not present in plant-based foods. option d is correct.
Step-by-step explanation:
Vitamin B-12, also known as cobalamin, is essential for various cellular processes including DNA synthesis and red blood cell formation.
The synthesis of vitamin B-12 occurs only in bacteria, and it is not produced by plants. Humans obtain B-12 primarily through their diet, with animal products being the main source.
This includes items such as meat, fish and seafood, dairy products, and eggs.
Animal livers and muscle meats are particularly high in B-12 content. For those following strict vegetarian or vegan diets, fortified foods or supplements are often necessary to maintain adequate vitamin B-12 levels, as plant-based foods typically do not supply this nutrient.
Therefore, the correct answer to the question 'Vitamin B-12 is supplied almost entirely by:' is d) Animal products.