The answer is; A.
This occurs for a cell that has no ion channel receptors. These cells have surface receptors that change conformation on the binding by an extracellular ligand on the active site. This change in conformation results in an initiation of a chain cascade of biochemical reactions inside the cell. An example is cells responding to insulin and glucagon hormone that bind on their surface receptors that invokes cell responses that regulate blood sugar levels in the blood.