*Which of the following pharmacological mechanisms is most likely responsible for the observed change in the dose-response curve?* A) The second medication acts as a competitive agonist, increasing the overall receptor activation. B) The second medication acts as a competitive antagonist, shifting the dose-response curve to the right. C) The second medication acts as a noncompetitive antagonist, reducing the maximum receptor activation. D) The second medication acts as a partial agonist, partially activating the serotonin receptor.