Extra exam question E9F06

WhyAn air-insulated, parallel conductor transmission line electrically 1/2 wavelength long at 14.10 MHz has an approximate physical length of 10.6 meters. A half-wavelength at 14.10 MHz in free space is about 10.64 meters, and an air-insulated parallel-conductor line has a velocity factor close to 1 (typically around 0.97 to 0.98), so the physical length needed is very close to that free-space half-wavelength figure, approximately 10.6 meters, answer C. The other figures don't match this calculation once the near-unity velocity factor of air-insulated open-wire line is properly accounted for.