The best option from the list would be that fairs took place "once a month" in the Middle Ages, but it usually had more to do with the changing of the seasons than with the start of each month.
Slavery was the main topic of the Lincoln-Douglas so it would be D! Hope this helps! :)
The symptoms of farmworker exploitation and the more flamboyant aspects of farmworkers’ efforts to gain fair contracts from the growers have become quite well-known. Much less known by equally important is a story which deals with the nitty-gritty of the farmworkers’ struggle for economic dignity: their efforts to form a nation-wide farm workers union.
Congress outlawed the foreign slave trade in 1808, but there was a high birthrate among enslaved women, which meant the enslaved population would keep on growing. When the cotton production rose, everybody wanted to have skates to harvest their cotton for them, and the fact that the enslaved population was growing was even more convenient for them. So why did they become to dependent? Because farming cotton was hard work that the Southerners did not want to do. The best solution for them was to buy slaves, who would do the hard work for them and cost them barely nothing.
When cotton gun was invented in 1793, the impact was profound. In 1792, the year before cotton gin was invented, the South produced only about 6,000 bales of cotton annually. In 1801 the annual production reached 100,000 bales which is almost 17 times as much as it was nine years ago. The invention of cotton gin also cause people to be more in need for slaves; between 1820 and 1850, the number of slaves in the South rose from 1.5 million to nearly 4 million.
Hope this helped! :)