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Many of the problems we face today are not so new as we think they are. And some of our modern solutions are not so new, either. The problem of energy shortages and the solution of using solar energy go back at least to early Greek cultures. The climate in the coastal areas of Greece 2,500 years ago was characterized by cool winters, much as it is today. At that time, the Greeks heated their homes with small, charcoal-burning heaters. In other words, wood (which is used to make charcoal) was their primary source of energy. However, by the fifth century B C fuel shortages had become common be- cause, in many parts of Greece, the firewood in the forests had been depleted. Once the supply of fire- wood from the local forests ran out, people began to use the wood from olive groves as fuel. But this solution had its own problem. It reduced the olive crop, a valuable resource to the Greeks. By the fourth century B C, the city of Athens banned the use of olive wood for fuel. Wood had to
A. using wood from the olive groves in ancient Greece was a sensible solution to the fuel problem
B. using passive solar energy was more expensive than using wood in ancient Greece
C. the ancient Greeks planted new forests to replace the ones they cut down for firewood
D. the concept of using passive solar energy has been around since at least the fourth century B C