During Cotransport of Glucose with Sodium, Sodium Increases the Affinity

During cotransport of glucose with sodium, sodium increases the affinity of the carrier molecule for glucose when the binding site is facing which side?

A) Both sides are affected equally.
B) the extracellular fluid
C) Cotransport does not involve changes in affinity of the carrier molecule.
D) Sodium decreases the affinity of the carrier for glucose; it does not increase affinity.
E) the intracellular fluid