Explanation: Radar frequency bands are designated by letters (e.g., L, S, C, X, Ku, K, Ka) as a historical convention that originated during World War II for military radar systems. Each letter corresponds to a specific range of microwave frequencies. The X-band is specifically defined as the frequency range from 8 to 12 GHz. This band is widely used for various radar applications, including weather surveillance, maritime navigation, air traffic control, military fire control, and synthetic aperture radar (SAR), due to its good balance of antenna size, resolution, and atmospheric propagation characteristics. Options A, B, and C represent different, lower frequency radar bands. For example, 1-2 GHz (A) is typically L-band, 2-4 GHz (B) is S-band, and 4-8 GHz (C) is C-band. Each of these bands has different properties and applications distinct from X-band.