我国水稻栽培历史悠久, 水稻作为重要的粮食作物被列为五谷之首。袁隆平先生成功培育出优质杂交水稻,为人类解决“温饱”问题作出重大贡献。目前已知水稻种植最早出现于下列哪一地区(  )

如图，在平面直角坐标系xOy内，第1象限存在沿y轴负方向的匀强电场，第Ⅳ象限以ON为直径的半圆形区域内，存在垂直于坐标平面向外的匀强磁场，磁感应强度为B．一质量为m、电荷量为q的带正电的粒子，从y轴正半轴上y=h处的M点，以速度v₀垂直于y轴射入电场，经x轴上x=2h处的P点进入磁场，最后以速度v垂直于y轴射出磁场．不计粒子重力．求：

Mr Green had a little boy. Every day had work he came home and played with his son.
One night ,while Mr Green was at work, he 1 that he had extra work to do for the evening ,and that he wouldn’t be able to play with his son.2he wanted to give the boy something to keep him3. So , looking around his office , he saw a 4with a large map of the world on the cover(封面). He got an 5 He removed the map , tore(撕) it up into small pieces and put all the pieces in his coat pocket.
When he got home , the little boy came running to him and was ready to play. Mr Green6that he had extra work to do and couldn’t play at the moment . Then he 7 all the pieces of the map and put them on the table . He said to the  boy,”8” was a map of the world, and  9th time you put it back together, my extra work will be finished, and we can 10”. Surely, this would keep the child busy for   11  , he thought.
About half an hour later the boy came to Mr Green and said,” Okay, it’s  12 . Can we play now?”
Mr Green said ,“That’s amazing!13did you do that?” The boy said, “It was14. On the back of the page was a picture of a man . When I put the man together the whole world fell into place.”

    Going to work by car is getting more expensive today because the petrol(汽油)is getting more expensive（贵）.People are looking for a cheaper way of transportation and they find out that it is a good choice(选择) to ride bikes to work.More and more return to bikes.

    Children often go to school by bike.But now more people are going to work by bike, too.“The bike is easy to use,”says Molly,“and it is also very cheap. It's a good choice for those who do business（生 意） like me.You can buy thirty bikes for the price of a small car. A bike doesn't use expensive petrol.”

    Mr.Brown goes to his hospital by bike every day. He says,“A bike doesn't cost so much money, and most families can have two or more bikes. Bike riding is good for our health. Today most people get fat because they don't get enough exercise. So I tell all my patients(病人) to buy bikes. Besides, in big cities it's usually quicker to travel by bike than by bus or car. Car drivers can do nothing but get angry when there is a traffic jam（有交通阻塞）.