Which statement describes signaling at the physical layer?

Question:
Which statement describes signaling at the physical layer?

• Sending the signals asynchronously means that they are transmitted without a clock signal.
• In signaling, a 1 always represents voltage and a 0 always represents the absence of voltage.
• Wireless encoding includes sending a series of clicks to delimit the frames.
• Signaling is a method of converting a stream of data into a predefined code

Exam with this question: CCNA 1 (v5.1 + v6.0) Chapter 4 Exam Answers