Which is the most expensive and least commonly used method of providing water to areas that need it?

Where does the availability of water pose the greatest problem

How long does it take for saturn to orbit the sun?

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