已知椭圆E： $\frac{x^2}{a^2}+\frac{y^2}{b^2}$ =1（a＞b＞0）与两条平行直线l₁：y=x+b与l₂：y=x﹣b分别相交于四点A，B，D，C，且四边形ABCD的面积为 $\frac{8b^2}{3}$ ，则椭圆E的离心率为（   ）

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    The Roses（罗斯一家）like having picnics on Sundays. This Sunday they want to go to the Red Park. Jack and Mike, their sons, get up early in the morning. Jack puts on a shirt and jeans, and Mike puts on a T-shirt and jeans. They also put on their running shoes. After that they help their mother put bread, milk, eggs and some fruit in a basket and carry it to the car. Mrs. Rose also takes four glasses of juice with her. The little dog Jerry is running after her. It wants to go with them, too. They are all very happy.

下列各式计算正确的是（   ）

某学者说：“农民造反者……长歌涌入金陵，开始建造人间小天堂，曾是他们的喜剧；天京陷落……则是他们的悲剧。”“他们”从“喜剧”走向“悲剧”的根本原因是

劈尖干涉是一种薄膜干涉，其装置如图13－7－17甲所示，将一块平板玻璃放置在另一平板玻璃之上，在一端夹入两张纸片，从而在两玻璃表面之间形成一个劈形空气薄膜，当光垂直入射后，从上往下看到的干涉条纹如图乙所示．干涉条纹有如下特点：(1)任意一条亮条纹或暗条纹所在位置下面的薄膜厚度相等．(2)任意相邻亮条纹或暗条纹所对应的薄膜厚度差恒定．现若在图甲所示装置中抽去一张纸片，则当光垂直入射到新的劈形空气薄膜后，从上往下观察到的干涉条纹(　　)

图13－7－17