The correct option is A Arginine and Histidine
Hopkins determined animals cannot synthesize seven amino acids. They are called essential amino acids (lysine, methionine, leucine, isoleucine, valine, tryptophan and phenylalanine). In human beings, essential amino acids are eight in number (additional threonine). Arginine and histidine are semi-indispensable, because they are slow to be formed in humans.