一个多边形的外角和是内角和的一半，则它是（   ）边形。

    In the past, most Chinese families have got one child in them. But recently, the government has relaxed the family planning policy, which means each couple are allowed to have two children. Would you like to have a brother or a sister who grows up together with you?

    Now please write a passage of about 80-120 words to introduce your opinion. The following points should be included:

    ⒈Is it necessary for a family to have more than one child? Give at least two reasons for it.

    ⒉What's the situation in your family? Are you the only child or not? List what makes you happy and unhappy.

    ⒊Give at least two suggestions to the families with two children.

课外阅读。

长大

小鸟在春天长大，蓝天是小鸟的妈妈。

鱼儿在夏天长大，大海是鱼儿的妈妈。

稻谷在秋天长大，土地是稻谷的妈妈。

雪人在冬天长大，娃娃是雪人的妈妈。

     所有的妈妈都爱孩子，所有的孩子才会长大。

据中央电视台对云南抚仙湖湖底古城考古的现场报道，科学家曾通过测定古生物遗骸中的 14C含量来推断古城年代，14C原子的核电荷数为6，相对原子质量为14.下列关于14C原子的说法中错误的是（    ）