The author implies that before the fifth century B C, （）

A．the climate was much milder in the coastal areas of Greece
B．the Greeks were very careful to replant their forests after they cut them
C．the Greeks were not concerned about conserving their energy sources
D．olives were not an important resource to the Greeks

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 be imported from farther and farther away, it more difficult to obtain and more expensive to use. About this time the Greeks began to build their houses facing south, so that the low sun in winter could penetrate and help heat the interiors. Excavations of ancient Greek cities suggest that large areas were planned so that individual homes could take maximum advantage of passive solar energy.