Final answer:
Radio has primarily become a local advertising medium, effective for reaching certain demographic segments and local markets without incurring high production costs.
Step-by-step explanation:
The correct statement about radio as an advertising medium is that radio has evolved into primarily a local advertising medium. With the advent of community radio and the focus of local stations on regional issues, radio advertising has found its niche in local markets. While nationwide network revenues contribute to the overall picture, the localized impact, especially in local elections or small markets, remains significant. It's also worth noting that radio does not involve high production costs in comparison to other media like television, making it an accessible medium for many local businesses. Moreover, while radio advertising's effectiveness may be hampered by the diversity of media channels available today, such as social media and the Internet, it still holds ground in specific demographic segments and localities. Lastly, the assertion that radio advertising results in lower reach and frequency due to high costs is not accurate; rather, its effectiveness varies based on the target audience and the locality.