When a Patient Asks the Nurse,"What Are Neurotransmitters?" the Nurse

When a patient asks the nurse,"What are neurotransmitters?" The nurse replies that neurotransmitters are:

A) "the chemical messengers that cause brain cells to turn on or off."
B) "small clumps of cells that alert the other brain cells to receive messages."
C) "tiny areas of the brain that are responsible for controlling our emotions."
D) "weblike structures that provide connections among various parts of the brain."