Final answer:
Radio's affordability allows for increased reach and frequency in advertising schedules, providing broad audience engagement, especially useful in local contexts. Option b.
Step-by-step explanation:
The relatively low cost of radio advertising time makes it an effective medium through which advertisers can build more reach and frequency (b) into their media schedules. Radio advertising offers the advantage of being a more affordable option compared to other media like television, allowing for the possibility of more frequent ads or reaching a wider audience with the same advertising budget. Moreover, radio can target local communities effectively and is particularly useful in the context of local elections, where the impact can be more pronounced. While not as targeted as narrowcasting approaches seen in new media, radio advertising still enables a connection with a broader audience.