Final answer:
Vegetarians need to include vitamin B12 in their diet as it is exclusively found in animal foods. Good sources of vitamin B12 include liver, eggs, meat, and fish.
Step-by-step explanation:
Strict vegetarians also need to include a reliable source of vitamin B12 in the diet, because it is found exclusively in animal foods. Foods such as liver, eggs, meat, and fish are good sources of vitamin B12. Vegetables like potato have relatively less amount of this vitamin.