Which of the following statements about guard features is true?

• A. The guard circuit illuminates Green when a call is received and turns Yellow after completion.
• B. The guard circuit remains Yellow for 5 seconds after the call is complete.
• C. The operator's transmission on a circuit illuminates Red.
• D. All of the above

Answer: (D)

Guard features use color-coded indicators to give you at-a-glance status of the circuit. When a call is received, the Green light signals you to monitor and indicates an active incoming call. After the call ends, the light turns Yellow, showing the guard period is in effect and you’re in the post-call state. That Yellow state lasts for a brief, fixed duration—5 seconds—to give you a moment to confirm the completion and prevent abrupt changes that could cause you to lose track of the status. If you are the one transmitting on the circuit, the Red light will illuminate to show the line is actively in use by your transmission. Taken together, these behaviors describe a coherent indicator system that communicates the full sequence of call, completion, and active transmission, so all of the above statements accurately reflect guard features.