Hold-short lines serve to indicate what boundary?

• A. The boundary where you may cross the runway without clearance.
• B. The boundary for exit taxiways only.
• C. The boundary you must not cross without explicit clearance to access the runway.
• D. The boundary for emergency vehicle parking.

Answer: (C)

Hold-short lines mark the boundary between a taxiway and a runway that you must not cross without explicit clearance to access the runway. They’re placed to prevent runway incursions by stopping aircraft before the runway until ATC says you may cross. When you’re cleared to cross, you proceed across the line; until then, you hold at the line and wait for permission. This boundary isn’t about exits to taxiways only or about emergency vehicle parking—it’s specifically about gaining access to the runway, which is why crossing without clearance is not allowed.