There was a man who had four sons. He hoped his sons could learn not to judge things too quickly. So he gave them a task in turn,____ (ask) them to go to see a pear tree at a distance____(separate).

    The first son set out in winter, the second in spring, the third in summer, and the____young)in autumn.

    When all of them returned home, they were called together____(describe) what they had seen. The first son complained the tree was____ (bend) and ugly. The second son said the tree was covered with buds(花蕾)and full of hope. The third son said it was full of flowers____smelled so sweet and that he had____seen such beautiful scenery. The last son disagreed____all or them, saying it was filled with fruits, full of life and content.

    The man told his four sons that they were all correct, but they only saw the tree in____season, He taught them that the value of a person could only be measure when all the seasons were over.

    If you give up in winter, you____(miss) the hope of spring, the beauty of summer, and the harvest of autumn in your life.

请用简要的语言解释材料一所指的历史事件及其收效？