What is the first reaction of the pentose phosphate pathway?
(a) Oxidation of glucose 6-phosphate to 6-phosphoglucono-δ-lactone
(b) Oxidation of 6-phosphogluconate to ketopentose ribulose 5-phosphate
(c) Reduction of 6-phosphoglucono-δ-lactone to glucose 6-phosphate
(d) Reduction of ketopentose ribulose 5-phosphate to 6-phosphogluconate