Answer:
Keeping lakes and rivers free of pollution.
Explanation:
Primary succession occurs when new land is formed or bare rock is exposed
The common geographic factor for Egypt and the fertile crescent were the big rivers, they made big alluvial deposits on their shores each year and allowed the people to have sufficient amount of food production. That opened the gates for civilizations to flourish in this places.
They came because of Rinderpest. Before coming to South America, Africans in Africa depended on cattle such as cows to thrive. But Rinderpest brought to Africa by foriegners began to spread, and the cattle started to suffered from fevers, inflammation in the brain and dysentery. They also had major problems with Europeans and their industries. So they decided to settle in South America.
Hope this helps :)
