The correct option is:
They can be linked back together to form an enzyme.
Amino acids are the building blocks of proteins, including enzymes. Once they enter a cell, they can be synthesized into proteins through a process called translation. The other options (forming lipids, sugars, or starches) are not correct as those involve different types of monomers (fatty acids for lipids, monosaccharides for sugars, and glucose for starch).