Explanation: Radar ranging fundamentally relies on the constant speed of radio waves, which travel at the speed of light (approximately 162,000 nautical miles per second or $3 \times 10^8$ meters/second in a vacuum/air). To determine the target's distance, a radar system measures the time it takes for a pulse to travel from the transmitter, reflect off the target, and return to the receiver. This means the pulse travels twice the distance to the target. 1. **Total Distance:** The pulse travels 10 nautical miles *to* the target and 10 nautical miles *back* to the receiver, for a total of 20 nautical miles. 2. **Speed of Light (Radar-specific):** A common conversion factor in radar is that radio waves travel approximately 1 nautical mile in 6.18 microseconds (one way). Therefore, for a round trip, it takes roughly 12.36 microseconds per nautical mile. 3. **Calculation:** For 10 nautical miles (round trip): $10 \text{ NM} \times 12.36 \text{ microseconds/NM} = 123.6 \text{ microseconds}$. This aligns perfectly with option C. Option A represents the round-trip time for just one nautical mile, while B and D are significantly incorrect magnitudes.