在探究压强与哪些因素有关时，小明猜想“压强可能与压力和接触面积有关”，为验证“压强是否与接触面积有关”，小明采用如图甲和图乙两种方法静止地挤压在两手指间来进行实验，下列说法中正确的是（　　）

    Everybody can suffer from stress．No matter what your age is，you can feel stressed out by things that are happening in your life．Teenagers，however，have many more opportunities to get stressed than people in any other age group．Being a teenager is hard．You are not a child any more，but you are not an adult，even though you have to deal with some very grown-up problems and decisions．Families can be one of the biggest causes of stress，such as problems with parents arguing at home．or problems with brothers and sisters．Teenagers also have a lot of stress from school，either from their teachers or from their friends．Some teenagers also feel stressed about choosing their education after high school．Getting a place at university can be very difficult and some cannot afford to go to university．The stress about getting a job when finishing school is hard for some teenagers．There are so many young people finishing school and not enough jobs for them．Sadly，there is nothing we can do to remove these causes of stress from the 1ives of teenagers，but you can learn the best way to deal with it．Talking to people is one of the best ways to deal with stress．It may sound simple，but it is true．A problem shared is a problem halved．

阅读下列材料：

材料一  古代时期的图像、殖民时期的文献以及一个多世纪的人类学田野调查，使我们了解到玉米神在玛雅神话中的重要地位。民族志资料不断提及这位神祗及其在其他中美洲社会群体中的对应体，……那些看起来平常世俗的玉米播种、耕作和制作食物的准备工作亦是玉米神话的重要方面。

         ——MichaelD．Carrasco《玛雅农业神话：玉米和人的生命轮回》

材料二  宗教信仰在玛雅文化中，扮演着重要的角色。近年来，透过铭文释读与雕刻装饰的综合解读，研究者发现山丘是玛雅人的重要崇拜之一。“山丘”一词厂泛的出现在地名、文献、雕刻装饰之中。同时，玛雅人将金字塔神庙看作是山丘。这些建筑物被设计成山丘，并且复制了神圣性地理景观到城市之中。藉由山丘崇拜，统治者增强了统治权威，塑造自己作为人间世界与超自然世界中介者的形象。

               ——蔡佾霖《地理景观与宗教：古典玛雅人的山丘崇拜》

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极坐标系与直角坐标系xOy有相同的长度单位，以原点O为极点，以x轴正半轴为极轴．已知曲线C₁的极坐标方程为 $\rho =2\sqrt{2}\sin \left(\theta +\frac{\pi }{4}\right)$ ，曲线C₂的极坐标方程为ρsinθ=a（a＞0），射线 $\theta =\varphi ,\theta =\varphi +\frac{\pi }{4},\theta =\varphi -\frac{\pi }{4}$ ， $\theta =\frac{\pi }{2}+\varphi$ 与曲线C₁分别交异于极点O的四点A，B，C，D．

（Ⅰ）若曲线C₁关于曲线C₂对称，求a的值，并把曲线C₁和C₂化成直角坐标方程；

（Ⅱ）求|OA|•|OC|+|OB|•|OD|的值．