B. are more difficult to control than point sources. This is because A. is wrong (point source), and C. is wrong, because it doesn't necessarily cost less or more to identify the sources. D. may be right, as non point sources are natural, such as snow melts or rain.
Answer:
when carbon dioxide level goes up.temp. goes down.and vice versa
answer:
it took 17,000 years for CO2 to go from 200 to 300 ppm.
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Answer:
Layer A is the crust and Layer B is the mantle.
