Ancient societies like the Mayans

Why have some historians rejected the labels bc and ad as laels for periods in world history

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.

Lucia drew a diagram to compare animal cells and plant cells. which label belongs in the area marked y? golgi body cell wall chloroplasts flagellum