如图，⊙O中，AB是直径，半径CO⊥AB，D是CO的中点，DE∥AB，求证：$\stackrel{\wedge }{EC}$=2$\stackrel{\wedge }{EA}$．

    My new Chinese teacher is Miss White. She is funny and kind. Her favourite food is salad because it is fresh and healthy. She can sing English songs and play the guitar. There is a lake in front of her house. Behind the house, there is a mountain. So she often climbs the mountain and plays some sports on the weekend. I like my Chinese teacher.

“近代文明之特征，最足以变故之道，而使人心社会焕然一新者，厥有二事，一曰人权说，二曰生物进化论。（陈独秀《吾人最后之觉悟》）”这表明陈独秀

实验室现有高锰酸钾、细铁丝、大理石和稀盐酸以及如图1的仪器．