Which parts of the COLREGs focus on sound and light signals?

The correct choice emphasizes the provisions outlined in Part C and Part D of the COLREGs. Part C specifically addresses the conduct of vessels in relation to collision avoidance, focusing on the use of sound signals, particularly in restricted visibility and in certain navigation situations. It outlines rules about the sound signals vessels must use to indicate their actions, such as horn blasts for maneuvering or signaling intentions.

Part D complements this by detailing the navigation lights and shapes that vessels are required to exhibit under various circumstances, such as anchored, underway, or in restricted waters. These signals, both visual through lights and auditory through sound signals, are crucial for ensuring safe navigation and preventing collisions at sea.

The other options do not correctly encompass both sound and light signals as specified in the COLREGs. Thus, the emphasis on Part C and Part D captures the full scope of regulations regarding these essential signaling methods.