Which of the following are visual references used by pilots for navigation?

C is the correct choice because landmarks and geographic features serve as vital visual references for pilots navigating in-flight. These elements provide pilots with tangible points of reference that can help them determine their position relative to the surrounding environment. Recognizing geographical features such as rivers, mountains, and towns allows pilots to visually confirm their location and ensures they stay on course, especially when flying under visual flight rules (VFR).

Flight plans and checklists, while important for overall flight management and safety, do not serve as immediate visual references during navigation. They are more about procedural guidance rather than visual cues. Air traffic control directives are instructions provided to pilots from air traffic controllers, typically involving routing, altitude adjustments, and other operational commands, which do not directly relate to visual navigation. Instrument readings, while essential for monitoring aircraft performance and conditions, rely on data transmission rather than visual cues outside the aircraft. Thus, the use of landmarks and geographic features is particularly effective for enhancing situational awareness in relation to navigation.