Indicate Which Characteristic of a Mediated-Transport System Is Referred to in Each

Multiple Choice

Indicate which characteristic of a mediated-transport system is referred to in each item by filling in the blank using the following answer code:
-If the concentration of substance X outside the cell continues to increase but the rate of substance X's transport into the cell remains constant, what characteristic is being exemplified?

A) specificity
B) saturation
C) competition