阅读下面的短文，从每题所给的四个选项(A、B、C、D)中，选出最佳选项。
A
The Great Wall of China is considered to be the only man－made project seen from the moon. Although it was once thought to have been built entirely during the Qin Dynasty( 朝代) between 221 and 208 BC, it is now believed to have been started earlier.
The 15－foot－high, 25－foot－wide, 1,500－mile－long structure was undoubtedly built to keep out invading enemies. To the common people of the empire, who had been forced to build the wall, it was not worth it, however. The wall, and other public works completed by the Qin Dynasty, had caused great losses on the wealth and human life of the country. As a result, an angry population rose up in rebellion（反抗）against the Qin Dynasty, and in 207 BC the Han Dynasty began.
Because of its rich history and magnificent appearance, the Great Wall attracts tourists, scientists, and historians to this day and will continue to do so for generations.
56. According to the author of this passage, the Han Dynasty was able to come into power because .
A. enemies were not effectively prevented from invading the empire
B. it had started the work on the wall and really controlled it all |
