周长为800m的正方形铁片，要在其上截出一个圆，该圆最大面积是（   ）

在划横线处填写正确的读音。

材料一、中国外交部发言人在2012年4月16日下午举行的例行记者会上说：“黄岩岛是中国的领土，中方要求这艘考古船（菲律宾）立即离开黄岩岛海域。”外交部发言人表示黄岩岛局势的主要原因是菲律宾方面侵犯了中国的主权，因为黄岩岛是中国的固有领土。

材料二、我国某月等温线分布图。

    Keeping a diary in English is one of the best ways to improve our English writing ability.

    Compared with other forms of writing, it is shorter and takes ____(little) time. It can help us to develop the habit of thinking in English.____we stick to this practice,____ (gradual) we'll learn how to express (表达) ourselves in English. In keeping a diary in English, we certainly run up against many ____ (difficult). In the first place, it often ____(happen) that we have trouble ____(find) proper words and phrases to give expression to our mind. And____ is very hard for us to put them into English properly.

    As far as I am____(concern), my suggestion is that we should always have a notebook and a Chinese­English dictionary within easy reach. We can also turn to our English teacher for help, if necessary. In short, I believe that it is ____great use to keep a diary in English for the development of ____ (we) writing skills.

① $\widehat{AE}$ = $\widehat{BF}$ ；

②△OGH是等腰三角形；

③四边形OGBH的面积随着点E位置的变化而变化；

④若BG=1﹣ $\frac{\sqrt{3}}{3}$ ，则BG，GE， $\widehat{BE}$ 围成的面积是 $\frac{\pi }{12}$ + $\frac{\sqrt{3}}{6}$ ．

其中正确的是____（把所有正确结论的序号都填上）