Answer : 3. "Nutrients"
Explanation :

Researchers recently discovered that FLVCR2, a protein, facilitates the transport of the essential nutrient choline into the brain. Choline plays an important role in cellular growth and metabolism, being present in both water- and fat-soluble forms. While the body can produce choline in the liver, dietary intake is necessary to meet daily requirements. Rich sources include meat, fish, dairy, eggs, as well as various fruits, vegetables, and whole grains.