①点P的轨迹关于y轴对称；

②存在b使得椭圆G上满足条件的点P仅有两个；

③|OP|的最小值为2，

其中，所有正确命题的序号是____．

阅读理解

   Everybody wants to be healthy. You know food is very important. There are lots of healthy food. You can have more bananas, apples, oranges, tomatoes and lettuce because fruit and vegetables are good for you. But don’t eat too much chocolate. It’s not healthy food. Healthy food can make you grow (生长) and make you strong（强壮的） and happy. Remember there is a saying—“An apple a day keeps the doctor away（远离）”. Sports can also keep you healthy. Get up early and do some sports every day. Don’t be lazy（懒惰的）. You will be healthy and happy.

丙酮（CH₃COCH₃）在某溶剂里，在催化剂作用下发生反应：2CH₃COCH₃（aq）⇌CH₃COCH₂COH（CH₃）₂（aq）取相同浓度的CH₃COCH₃，分别在40℃和60℃时，测得其转化率α随时间变化的关系曲线（α﹣t）如图所示．下列说法正确的是（　　）

用两个相同的加热器，分别对质量相等的甲、乙两种液体加热，忽略热量的散失，其温度随时间变化的规律如图所示，由图可以看出（）