下列现象属于原始农业出现重要标志的是（    ）

①农作物种植

②磨制工具

③家畜饲养

④聚落

⑤城市的出现

把一个圆形纸片剪开后，拼成一个宽等于半径，面积相等的近似长方形．这个长方形的周长是24.84厘米，原来这个圆形纸片的面积是多少平方厘米？

阅读短文，完成练习。

牛顿的故事

    伟大的物理学家牛顿是在外祖母家长大的。外祖母很疼他。牛顿8岁上学以后，外祖母有时给他一些零用钱，小牛顿一不买糖果，二不买玩具。他把钱积攒起来，买了锤子和锯。他喜欢自己动脑筋，做些手工制品。

    一天，小牛顿兴冲冲地跑到外祖母面前说：“外婆，你看这个。”外祖母一看小牛顿手里捧着一块木板，中间钉着一个钉子，四周画着一条条放射形的线条，外祖母问；“这是什么呀？”“太阳钟。太阳光把钉子的影子投到哪条线上，就可以看．出是什么时间了。”“是谁教你做的呀？”“是我自己想出来的。”小牛顿自豪地回答。

    牛顿长大以后，始终保持着善于思考、勇于创新的精神，取得了许许多多科学研究成果。

①用活性炭吸附的方法能使硬水转化为软水；

②为防止水污染，应禁止使用化肥和农药；

③用肥皂水可以鉴别硬水和软水；

④电解水生成氢气和氧气说明水由氢、氧元素组成；

⑤液态水变成水蒸气时，水分子变大．

    A boy and a girl were playing together. The boy had a lot of small glass 1. The girl had some candies with her. The boy told the girl that he would2her all his balls in exchange for (交换) her candies. The girl thought that was a good3.

    But the boy didn't give4of his balls to the girl. He kept the biggest and the5ball in his pocket and gave the others to the girl. 6the girl gave him all her candies.

    That night, the girl had a 7sleep, but the boy didn't sleep well. He kept thinking whether the girl had 8some candies from him.

    You think in the way you do things. If you don' t give your hundred percent(百分之百) in a relationship, you'll 9 keep thinking if the other person has given his or her hundred percent. This is true for any relationship.

    Give your hundred percent to everything you do and you'll find that you can always10a lot of happiness.