A tri-peptide has an amino acid composition (Lys, Phe, Pro). Dansyl chloride treatment produces Dns-Phe. The peptide is
The principle of enzyme catalysis and lipid structure explains that substrate affinity, transition state stabilization and phospholipid composition govern function. Hence Phe-Pro-Lys fits best because it reflects catalytic efficiency and membrane organization, as documented in authoritative sources on biochemistry.
Ref: Lehninger Principles of Biochemistry, Chapter 9, Lipids and Membranes, explains phospholipid components, glycerol, fatty acids, phosphate group and membrane structure providing foundation for lipid biochemistry.