Around 1800 (plus or minus about 5 years) is when it was estimated that the world's population had reached 1 billion.
The answer would be b) push factors
The body of water that the city of Los Angeles is located on is called the Los Angeles River. It now flows through a concrete channel on a fixed course, since it has been redrawn after many chaotic floods. The river is rarely used however for fresh water for the city, as it is now very polluted and has urban discharge in it's water, so the aqueducts in the city are now used for the fresh water mainly utilized in Los Angeles.
