What conditions must be met to announce over the radio?

The correct choice emphasizes the comprehensive conditions needed for making announcements over the radio during railroad operations. Announcing the signal aspect and location, authority changes, and arrival/departure times for passenger trains ensures that all relevant and operationally critical information is communicated clearly amongst crew members and other relevant personnel.

By including signal aspects and locations, it confirms the current state of the train's operation and ensures safety measures are adhered to. Authority changes are crucial for maintaining proper communication about who is in charge of operations, preventing any potential confusion or miscommunication that could arise in critical situations. Additionally, passenger train arrival/departure times are key for scheduling and coordinating activities around stations, ensuring that crew members, passengers, and station staff are all aligned and informed.

Overall, this multifaceted approach to radio communication guarantees that all necessary operational information is communicated effectively, promoting safety and efficiency within railroad operations. The other options lack this level of thoroughness and do not consider the range of information necessary for effective communication in the rail environment.