Can someone answer my geography question -_-

Explain the cause for movement river valley civilization to early industrial centers

Exactly what kind of weather conditions would a cold front produce?

Which ecosystem best fits the characteristics listed below? which ecosystem best fits the characteristics listed below? ii. seasonal migrations of millions of wildebeests, zebras, and elephants iii. large numbers of predators, such as lions iv. acacia trees and grasses a. the congo rainforest b. the african mangroves c. the serengeti grasslands d. the sahel