从水平飞行的直升机上向外自由释放一个物体，不计空气阻力，在物体下落过程中，下列说法正确的是（   ）

下列函数中是二次函数的有（）

 ①y=x＋ ；②y=3（x－1）²＋2；③y=（x＋3）²－2x² ；④ ．

以下哪一组实验材料必须自始至终保持在生活状态下的是（   ）  
①观察植物细胞有丝分裂            ②观察植物细胞的质壁分离和复原 
③用高倍显微镜观察叶绿体和线粒体  ④叶绿体中色素的提取和分离
⑤探究酵母菌细胞呼吸的方式                 

In England ,people don't often talk to each other when they travel. If you get on a bus or a train. you can see people sitting and looking out of the window. Other people may read books or newspapers.
When you meet English people, they often start a conversation by talking about the weather . So when you meet somebody in England, you can say, "Nice weather for the time of the year!"
"But it was a little cold yesterday, "somebody may answer.
"But it will get a bit warmer later,"you can say.
Talking like this, they will think,"How friendly you are!"