The Affinity of a Receptor for Its Ligand Is a Measure

The affinity of a receptor for its ligand is a measure of the

A) strength of binding between ligand and receptor.
B) percent of receptors on a specific target cell with bound ligand.
C) number of binding sites available for the ligand.
D) response produced in the target cell when the ligand binds to the receptor.
E) ability of the ligand to permeate the plasma membrane and reach its receptor.