The correct answer is Proteins.
Every protein in the body is constructed from smaller units called amino acids, strung together in long chains through what are known as peptide bonds. There are twenty standard amino acids that living cells use, and the particular order in which they are arranged gives each protein its unique three dimensional shape and job, whether that is forming muscle fibre, acting as an enzyme, or making up part of the immune system as an antibody.
None of the other options share this connection to amino acids. Carbohydrates are built from sugar molecules like glucose linked in chains, an entirely separate chemistry. Fats come from fatty acids combined with glycerol, again unrelated to amino acid structure. Vitamins form their own diverse group of organic molecules needed in small quantities for the body to function properly, but they are not assembled from amino acids the way proteins are.
Because amino acids are specifically the units that combine to make proteins, the correct answer is option 3, Proteins.