Final answer:
The inactivation of a cell-surface receptor depends on the binding affinity of the receptor and the concentration of ligand surrounding the cell, as well as phosphatase activity which removes phosphate groups during inactivation.
Step-by-step explanation:
Inactivation of a cell-surface receptor depends on several factors, but among the choices provided, the correct answer is both the binding affinity of the receptor and the concentration of ligand surrounding the cell. The binding affinity indicates how strongly a ligand binds to its receptor, which can influence the duration the receptor is activated or inactivated. Simultaneously, the concentration of the ligand around the cell affects the likelihood of the ligand binding to the receptor in the first place, and thus can also influence the receptor's activation state. The inactivation of the receptor often involves phosphatase activity to remove phosphate groups that were added during activation, returning the receptor to its inactivated state.
It is worth noting that factors like receptor internalization, degradation, and the production of inhibitory proteins can also play a role in receptor inactivation, even though these options were not provided in the given choices.