Summer vacation is coming. Here are some ideas for planning your vacation.

    First of all, joining a club is a good choice! We have a music club, a sports club and an art club. It's good for your future development and the teachers in the clubs can give you good advice.

    Doing something good for the society is also great. Here we'll offer(提供) a volunteer program for you. You may find you teens（青少年） can also make the world better. If you want to be a volunteer, call us at 682-679 from Monday to Friday.

    Have you ever had the experience of living with another family? Here's a program –“Meeting a New Family” to have two families exchange their children for a certain time. Isn't that exciting? Join us!

    A summer camp is still popular today. We are going to hold an English summer camp this year. There you can not only make friends but also improve your English. You can practice English in different games, speech contests and so on. Do you like it?

历史是可以求真的，因为   (      )

①历史记载的客观性是存在的 ②人类认识能力的提高，事业的开阔 ③研究方法的多样化④技术手段的不断进步

如图，“美国东北部工业区图”和“我国京津唐工业区图”，完成下题。

面对环境污染严重、生态系统退化的严峻形势，党的十八大报告指出，必须树立尊重自然、顺应自然、保护自然的生态文明理念．请回答下列问题．

（1）生态系统是在一定的空间范围内，____ 和____ 所形成的统一的整体．一片森林、一片草原、一个湖泊等等，都可以看作一个个生态系统．如图要构成一个生态系统还需要阳光、水分、空气等部分，以及____ ．图中有机物含量最多的生物是____ ，它是生态系统中的____ 者．

（2）图中共有____ 条食物链，这些食物链彼此交错形成了____ ．如果图中生物所在的这个生态系统被有害农药污染，那么，生物体内含有的农药浓度最高的生物是____ ．

（3）在生态系统中，虽然各种生物的数量是在不断变化的，但在一般情况下，各种生物的数量和所占比例是相对稳定的，这说明生态系统具有一定的自动____ 能力；图中，如果大量捕捉野生青蛙和鸟类，一段时间内，会导致蝗虫的数量____ ，使水稻减产．

已知f（x）是二次函数，且f（0）=0，f（x+1）=f（x）+x+1，

（1）求f（x）的表达式；

（2）若f（x）＞a在x∈﹣1，1恒成立，求实数a的取值范围．