Answer:
B
Explanation:
There are 7 billion people in the world and we approached that number in 2011.
I would say that housing availability, inadequate services, pollution and migration from rural areas all present challenges to the regional urban areas but not reduced population. If there is migration to the cities then these above three problems must be dealt with to accommodate the new citizens.
Both Radioactive dating of rocks retrieved from the world and Comparing cratering rates on one world to those on another.
Geologists can find the relative age of impact craters on a world because
the ones on top must be younger.
Scientists know the history of Earth's magnetic field because the magnetic field gets frozen into rocks, and plate tectonics spreads them out.
Hope it helps