The correct option is D Tryptophan
Those amino acids which cannot be synthesized in our body and must be obtained through diet are called essential amino acids.
Essential amino acids are Histidine, Tryptophan, Phenylalanine, Methionine, Threonine, Lysine, Arginine, Isoleucine, Valine and Leucine.
Hence the correct option is Tryptophan.