三个体积和质量都相等的空心铝球、铜球和铁球（ρ_铜>ρ_铁>ρ_铝），将它们的空心部分注满水后，则质量最大的是  （    ）

    “I will think of it.” It is easy to say this， but do you know what great things have come from thinking?

    Sir Isaac Newton was sitting in his garden when he saw an apple fall from a tree. He began to think and tried to find out why the apple fell. Then he discovered how the sun， moon， and stars are kept in their places.

    A boy named James Watt sat quietly by the fire， watching the lid of the kettle move up and down. He wanted to find out why the steam in the kettle moved the lid. From that time he went on thinking and thinking. And when he became a man， he improved the steam engine (蒸汽机) so much that it could easily do the work of many horses.

    James Ferguson was a poor boy. Once， seeing the inside of a watch， he wondered. “Why should I not make a watch?” But how could he get the materials to make the mainspring (钟表的主发条)? He soon found he could make it with whalebone (鲸骨). He then made a wooden clock which kept good time. His motto (座右铭) was “I will think of it.” And he made his thoughts useful to himself and the world. 

    Boys and girls， when you have a difficult lesson to learn， don't lose heart， and don't ask someone for help before helping yourselves. Think， and by thinking you will learn how to think to some purpose.

判断正误。

维也纳森林的面积是370万公顷，占国土的44％。（    ）

    Have you ever been sad because of failure? Please remember, for quite often achieving what you set out to do is not the most important thing.

    A boy decided to dig a deep hole behind his house. As he was working, a couple of older boys stopped by to watch. “What are you doing?” asked one of the visitors. “I want to dig a hole all the way through the earth!” the boy answered excitedly. The older boys began to laugh, telling him that digging a hole all the way through the earth was impossible. After a while, the boy picked up a jar. He showed it to the visitors. It was full of all kinds of stones and insects. Then he said calmly and confidently, “Maybe I can't finish digging all the way through the earth, but look at what I've found during this period!”

    The boy's goal was far too difficult, but it did cause him to go on. And that is what a goal is for－to cause us to move in the direction we have chosen, in other words, to cause us to keep working!

    Not every goal will be fully achieved. Not every job will end up with a success. Not every dream will come true. But when you fall short of your aim, maybe you can say, “Yes, but look at what I've found along the way! There are so many wonderful things having come into my life because I tried to do something!” It is in the digging that life is lived. It is the unexpected joy on the journey that really makes sense.