Spring is coming．People in different countries like different outdoor activities．Leo，a reporter from Learning English in interviewing（采访）some students．Here is what they have said．
    Mary （13, America）　　
    I want to go out of the city to a beautiful field. It's happy to smell beautiful flowers, touch green grass and take some photos. And I like to have a picnic in the field, It's interesting!
    Jim （14, Canada）　　
    The weather turns warmer and they days become longer in spring. It's a good time to go camping. It would be fun to sleep in a tent. I enjoy the comfortable weather too.
    Tony （13, England）
    In spring, I like going cycling alone. It can not only make me enjoy the beautiful season but also help me became stronger. I can write something about what I see on the way.
    Wang Fang （12, China）
    I'm good at making all kinds of kites. And in spring. I like flying kites with my family or my friends in the park. One of us holds the kite. and another one catches the line. It's exciting to see the kite flying high in the sky.

阅读下面的文字，完成第（1）～（4）题。

    动物在睡眠时，大脑能像人脑那样发出电波，也会做梦。如猫在睡觉的时候会竖起耳朵，嘴边的长须会颤动。有时它还会轻轻地叫几声，好像在追捕什么目标似的。鹦鹉睡觉____①____把头藏在翅膀下面，____②____也会发出很低的叫声。除了猫和鹦鹉之外，马和狗等家chù，以及其他一些哺乳类动物也会做梦。动物的梦有多有少。蝙蝠、老鼠比人更易做梦。③鸟类很少做梦，爬行动物也很少做梦，因为④它们必须随时保持对敌人的警告，以便能够及时逃脱。   

方程 ﹣ =0的解是____．