Absence of which of the following enzyme in humans is responsible for the inability to synthesize ascorbic acid?

Uronic acid pathway is an alternate pathway for oxidation of glucose without ATP formation. Fig: Uronic acid pathway An intermediate (L-gluconate) of this pathway can be used for the synthesis of ascorbic acid in plants by enzyme L-gulonolactone oxidase. However, In human beings and other primates, as well as guinea pigs, bats, and some birds and fishes, ascorbic acid cannot be synthesized because of the absence of L-Gulonolactone oxidase.