The correct answer is: A. Muscles.
Goosebumps are caused by the contraction of tiny muscles at the base of each hair follicle. These muscles are called arrector pili muscles. When they contract, they pull the hair upright, which causes the skin to become bumpy.
Goosebumps are often caused by cold temperatures, but they can also be caused by fear, excitement, or stress. They are a natural reflex that helps to trap heat in the body.
The arrector pili muscles are controlled by the sympathetic nervous system, which is part of the autonomic nervous system. The sympathetic nervous system is responsible for the “fight or flight” response. When the sympathetic nervous system is activated, it causes a number of physiological changes, including the contraction of the arrector pili muscles.
Goosebumps are a harmless phenomenon, but they can be embarrassing or uncomfortable. If you are concerned about your goosebumps, you can talk to your doctor.