As a general rule to follow, what does it mean when you see a red marking on the safety mechanism of your firearm?

Which of the following is an example of the endocrine system maintaining homeostasis? detecting a pain stimulus and sending a signal to the spinal cord to perform an automatic response discharging an excessive amount of hormones in the blood and not sending a signal to stop production releasing hormones that speed up heart rate and blood pressure while slowing body functions like digestion and growth using sense organs to get information about the outside world and direct an appropriate body response release