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

The parts of the COLREGs that focus on sound and light signals are indeed Part C and Part D. Part C outlines the rules concerning the conduct of vessels in restricted visibility, and it includes regulations about the use of sound signals to signal intentions or actions when visibility is poor. Part D covers signals to be used in various situations, including navigational signals and light signals, helping to communicate the presence and intentions of vessels under different circumstances.

Part A and Part B primarily detail the general responsibilities and definitions, while Part E deals with the obligations of vessels and communication protocols that are not specifically about sound and light signaling. Therefore, the correct answer reflects the sections that explicitly cover the use of sound and light for communication on the water, highlighting their importance for safe navigation.