4. E-stops are: a. Located in the tunnel. b. Turn off power to all tunnel equipment. c. Emergency stops. d. All of the above

The correct answer is d. All of the above.<br /><br />E-stops, or emergency stops, are devices used to quickly and safely shut down machinery or equipment in the event of an emergency. They are typically located in areas where they can be easily accessed, such as in tunnels or other confined spaces. When an E-stop is activated, it can turn off power to all tunnel equipment, ensuring that all systems are shut down and safe to operate.