Final answer:
A bowl of whole-grain cereal is the best source of thiamin out of the given options, due to the high thiamin content in whole grains. Thiamine is a water-soluble vitamin that must be regularly included in the diet as the body cannot store it for extended periods.
Step-by-step explanation:
The best source of thiamin among the options provided is D) a bowl of whole-grain cereal. Thiamine, also known as vitamin B1, is critical for energy metabolism in the body and has its richest sources in whole grains, along with other foods like nuts, seeds, pulses, and animal products. Since a bowl of whole-grain cereal predominantly consists of whole grains, it is likely to offer a higher content of thiamin compared to the other options listed, such as a fruit salad, a baked sweet potato, or a glass of milk.
It is important to note that thiamine cannot be stored in the body for long periods and is excreted in the urine, necessitating a regular dietary intake. Some food sources rich in thiamin include rice bran, wheat bran, nuts, seeds, beans, lentils, fish, meat, and milk. In contrast, vegetables like potatoes contain less of this vitamin.