Final answer:
VORs without voice capability are indicated by the letter 'N', which is option C. These are navigation aids that offer no voice communications to aircraft.
Step-by-step explanation:
VORs, or VHF Omnidirectional Range navigation systems, are a type of radio navigation system for aircraft that enables them to determine their position and stay on course via radio signals transmitted by a network of fixed ground radio beacons. VORs with no voice capability, meaning they do not provide voice communications alongside navigation signals, are indicated by the letter 'N'. This means that the correct answer to the question is option C) N.