The answer is B)High- rise buildings...
Yes. The stocket market crash caused people to lose their life savings and they became poor, causing the Depression.
D) about a quarter of Southerners had enslaved workers.
Not everyone in the South operated with slaves as their labor force. There were also smaller family farms and such. But those who did hold slaves in operating plantations held large numbers of slaves, and so the institution of slavery was a gigantic part of the Southern economy.
They possibly tried to document their events and what happened in their lives