Explanation: Before making a transmission, an operator should always monitor the chosen frequency to ensure it is not currently in use. This practice is fundamental to good amateur radio operating and is crucial for preventing interference (QRM) with other stations. By listening first, you can confirm the channel is clear, allowing for polite and efficient shared use of the limited radio spectrum. This aligns with the FCC's emphasis on avoiding harmful interference. The exception for distress calls (B) is vital: in emergencies, immediate transmission takes precedence over monitoring. Option A, checking equipment calibration, is part of overall station readiness but not the immediate step to prevent interference on a specific frequency. Options C and D, asking or notifying by transmitting, both involve transmitting *without* knowing if the frequency is clear. This action itself could cause interference and disrupt an ongoing conversation, defeating the purpose of trying to be courteous. Always listen before you transmit.