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$\stackrel{\wedge }{EA}$．

                                                                                        Everyone (人人)needs to be healthy.
   Do you eat healthy food every day? It’s important (重要)for your health. You need fruit, like oranges, apples and bananas. “ An apple a day can keep away（避开） the doctor (医生).” You also need vegetables, like carrots and broccoli. Fruit and vegetables are good for our health. But don’t eat lots of chocolate. It’s not good healthy food. What about dessert? Don’t eat lots of dessert because it’s not good for your health. Many people eat lots of chocolate and dessert, so they are unhealthy. Sports can also keep you healthy. Play sports every day. Don’t be lazy. You can be healthy.

在中国近代史上国共两党的合作都并非偶然的结果，都是在一定的历史条件之下，在共同的利益基础之上，以追求共同的或者相对一致的政治目标为出发点而展开的合作。其共同的利益基础指的是（    ）