群落演替的总趋势是（）

人口增长过快产生的危害是（　　）

    An village had a1tradition. At the beginning of every year, any boy who had reached the age of majority(the state of legally being an adult) was given land and money to build a home. The boy had to 2 his home before winter. If this home failed to endure the cold weather in winter, the villagers could not 3him in any way.

    On 4 Paul and Marc reached their majority. They 5 theri land and money and decided to search nearby villages for ideas on building their homes. In each village, they found the nicest 6and talked to the owners. Each owner gladly offered 7 .

    After Marc saw several homes, he  8the best ideas and went back to his own land. Paul,  9, continued collecting more ideas. Soon he had so many great ideas that he began to 10 some of them. And he always believed he could find even better ideas in the next village.

    Marc began building his home. He had several 11 starts, but his home gradually rose from his land. By fall, Marc had finished his home. It wasn't perfect, but it was strong and he could 12 it later. Paul enjoyed all the beautiful homes and 13 with home owners. The first snow came and Paul, realizing he was running out of time.14back to his land. He built the best home he could in the time he had, but it was 15. The first winter storm destroyed his home and he froze to16 . The villagers mourned for him.Marc  17 the winter. Each year, Marc searched for other good ideas he could use to make his own home look better. He became a leader in the village,18a family, and lived a happy and content life.

    We all build and improve our own mental homes. It's  19 and fun for us to search for ideas from other mental home owners ,but we only improve our own mental home if we actually 20 the best ideas.

    Once upon a time, there was a millionaire who loved money more than the other things in the world. He didn't know exactly how much he had, so he took on a little girl to count all his money for him.

    It took the little girl six days to count all the money. When she told the millionaire that he had forty-two million dollars, he was wild with joy and asked, “How much money do you want?” He thought she was only a child and he could give her less money.

    The girl said, “Well, I worked for six days, so I think you should pay me for six days. Give me two pennies for the first day. Each day after that, just give me the amount you give me the day before, multiplied(乘) by itself.”

    The millionaire thought that in this way he would only have to give her a few dollars. What a foolish girl!

    On the first day the millionaire paid her two pennies, and on the second day, two pennies times two pennies, or four pennies.

    Each day after that, he gave her the number of pennies he had given her the day before, multiplied by itself. And by the sixth day the foolish millionaire had to give the clever girl all his money.

    Long long ago, a millionaire loved money than anything ____ in the world. One day he took on a girl to count his money. The girl spent six days in ____ his money. The millionaire asked the girl how much money he should ____ for what she did. The girl answered he should give her the amount he gave her the day before, multiplied by itself.

    The millionaire ____ with the girl. He thought the girl was a ____. In fact, the girl was so clever. The millionaire had to give the clever girl all his money.

下列关于蒸发和沸腾的说法正确的是（    ）