“忆昔开元全盛日，小邑犹藏万家室”反映的是我国古代经济重心南移的现象。（    ）

根据材料内容，选择正确答案。

    An old man died and left his son a lot of money. But the son was a foolish young man, and he quickly spent all the money, so that soon he had nothing left. Of course, when that happened, all his friends left him. When he was quite poor and alone, he went to see Nasreddin, who was a kind, clever old man and often helped people when they had troubles.

    "My money has finished and my friends have gone," said the young man. "What will happen to me now?"

    "Don't worry, young man," answered Nasreddin. "Everything will soon be all right again. Wait, and you will soon feel much happier. "

    The young man was very glad. "Am I going to get rich again then?" he asked Nasreddin.

  "No, I didn't mean that," said the old man. "I meant that you would soon get used to being poor and to having no friends. "

“一方水土养一方人”．受自然环境的影响，我国北方地区、南方地区的人们在生产和生活方式上有很大的差异．据此完成下题．

建高楼时首先要打好地基，原相同高度的相同地桩，经打击后某一瞬时三个地桩所处的位置如图所示，打桩时，三个重锤中　____ 　锤的做功本领最大．如果A、B两锤的质量相同，则刚开始下落时，____ 锤的高度要低一些，如果B、C两锤刚下落时的高度相同，则____ 的质量要大一些．