Cataracts caused parts of the riverbed today out.
Id say C but in reality it was more profitable because farmers had to pay slaves next to nothing if not anything and could have multiple workers in poor conditions so mass amounts of free workers saved them money and they could work them 24 hours a day until they dropped making the process go faster producing more than other competing farms. A sad truth from our past.. hope this helps!
“era” refers to a period of time characterized by events in a chronological order.
“Period” can refer to a short interval of time or a very long interval of time.