What is a retentive timer (RTO) or retentive memory in timers, and when is it used?

What is a retentive timer (RTO) or retentive memory in timers, and when is it used?

• A. It resets elapsed time when input resets.
• B. It preserves elapsed time when input resets; used to accumulate total time across multiple activations.
• C. It cannot accumulate across activations.
• D. It preserves elapsed time across activations and can accumulate total time.

Answer: (D)