Which of the following pairs of compounds are interconvertible in the liver by a single polypeptide chain containing two different catalytic sites ?

Question

( A ) 3-phosphoglycerate and phosphoenolpyruvate
( B ) glucose and glucose 6-phosphate
( C ) phosphoenolpyruvate and pyruvate
( D ) fructose 6-phosphate and fructose 2,6-bisphosphate