In Which of the Following Is Cell Signaling Prevented

In which of the following is cell signaling prevented?

A) The nicotine in cigarette smoke binds to and activates the acetylcholine receptor in plasma membranes of neurons in the brain.
B) Proteins on the surface of cells in taste buds called umami receptors bind to glutamates and nucleotides in food, which changes the membrane potential of these cells and tells the brain, "This is savory."
C) Allergy medicines, which are called antihistamines, bind to and block histamine receptors to keep fluids in capillaries that would normally be released and cause stuffy noses and watery eyes.