Emma is a 25-year-old woman who has been following a vegan diet for two years and has not consumed any food from animal sources. Her food intake on a vegan diet has been well balanced. She generally follows Canada’s Food Guide by consuming a variety of vegetables including spinach, romaine lettuce, broccoli, carrots, sweet potato, squash, tomatoes and sweet peppers, and fruits like berries, bananas, apples, melons, and pears. She consumes only whole grains, such as whole-grain breads, oatmeal and brown rice, and chooses her proteins from nuts, seeds, and a variety of legumes. She takes no supplements. When Emma visits her doctor for a check-up, she orders blood work to assess Emma's vitamin B12 status and finds that Emma’s blood levels are insufficient, i. e. low but, fortunately, not yet so low that she is considered deficient.
Why were Emma's vitamin B12 levels low?

a. Vitamin B12 is a vitamin that is rare in the Canadian food supply and it is hard for vegans, vegetarians, or non-vegetarians to get enough of it.
b. The nuts and seeds that Emma eats contain chemicals that interfere with the absorption of vitamin B12.
c. Vitamin B12 is found mainly in foods of animal origin that Emma has not consumed for two years.