The delays change _______ during reception of the echoes.

• A. Abruptly
• B. Continuously
• C. Periodically
• D. Randomly

Answer: (B)

Delays are governed by time-of-flight, which is a continuous quantity determined by how far the echo has to travel and back. As the receiver processes the incoming signal, the relevant echo energy from reflecting surfaces arrives over a span of time, and the observed delay changes smoothly rather than in jumps. Even if targets move, they do so in a way that makes the delay shift gradually during the reception window. That's why the delays change continuously during reception.

Abrupt changes would require an instantaneous shift in distance, which isn’t how the reception window unfolds. Periodic would imply a repeating pattern, and random would imply no pattern at all; neither describes the orderly, time-based nature of echo delays during a single reception.