How do polar bears protect themselves from predators

What contribution did the pilgrims make to the development of american government

According to greenville why does great britain have a large debt and who should pay that debt? ?

The rise of advertising in the 1920s. i am good with seeing how advertisements shape the roaring twenties and how it developed a new way of life through modern days. but i am not sure what the details of advertising in the 1920s were. if possible can you send me links (preferrably credential links) to sources that maybe show like the first company to start advertising through the radio, how advertising benefits (statistics graphs), etc.