The united states has a federal system of government. what does that mean? a. the national government is controlled by a small group of people b. local government have most of the power c. the national government and the states share power d. the national government has most of the power

Which was the cause of the rise of the persian empire?

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.

Why do many scientists suppose the land bridge theory of migration?