关于腰神经根病硬膜外注射类固醇治疗的叙述，正确的是()A．可改变患者长期的结局 B．

It was a cold winter afternoon before Christmas. My parents and I sat on the bench in Washington, D.C.’Union Station, waiting for the train. Inside the waiting hall were many people.

A boy sat nearby. His worn jacket, pale face, dirty hands all seemed to tell me that he was homeless.

“He must be cold and hungry. Maybe I should help him,” I said to myself.

Just at that moment, a well-dressed young couple walked towards him.

“Excuse me,” the man bent down. “My wife and I bought two meal boxes but one was enough for us. We hate to waste good food. Can you help us out and put this to use?” he handed the boy a meal box.

The boy thanked them and opened the box with joy and care. Suddenly he stopped. In the direction to which he looked, I saw an old man in rags-in a worn sweater, worn trousers and open shoes, entering the hall.

Putting the meal box aside, the boy stood and helped the old to his seat. He took off his jacket and covered it on the old man’s shoulders, saying, “A gentleman brought me this warm meal but I just finished eating. I hate to waste good food. Can you help me out?” He placed the still-warm meal box in the old man’s hands without waiting for an answer.

“Sure, son, but if only you share that sandwich with me. It’s too much for a man at my age. ”

We were all touched. Dad went away and soon returned with cups of hot chocolate and a big pizza. Mum and dad went up to those rags, “Excuse me…”

I rushed into a KFC and took out my pocket money. It was so cold that afternoon but I felt much warmer than I had ever thought possible.

小题1:Who gave the boy a meal box?

A．The young woman.

B．The old man.

C．The young man.

D．Mum and Dad.小题2:Why didn’t the boy have the meal?

A．He was not hungry.

B．He wanted to help the old man.

C．He didn’t like the food.

D．He saw a sandwich in the meal box.小题3:What did the writer most probably do at the end of the story?

A. He bought some food for the homeless.

B. He told his story to the people in the KFC.

C. He gave his pocket money to the homeless.

D. He asked the other passengers to help the homeless.

目标成本战略

如图所示，平面直角坐标系xoy内，在x≤0的区域内分布着匀强电场，其等势线如图中虚线所示（相邻等势面间的距离相等）．在A点源源不断的产生速率为零、质量为m、电荷量为+q的粒子，经电场加速后从O点进入一个圆形的匀强磁场区，其磁感应强度为B，方向垂直纸面向里，其半径为R，直径OB在x轴上．在x=4R处有一个垂直x轴很大的光屏，与x轴的交点为C，粒子打在光屏上可出现亮点．设粒子的重力不计，A点所在的等势面电势为零，D点的电势为

（1）求从A点产生的粒子经电场和磁场后，打在光屏上的位置．

（2）若将圆形磁场区以O点为轴，整体逆时针将OB缓慢转过90度角（与y轴重合），求此过程中粒子打在光屏上的点距C点的最远距离．

解放前担任中山大学师范学院音乐教授，解放后担任中央音乐学院首任院长，著名的小提琴家和中国小提琴音乐的开创者是谁？

学习方法的指导主要有哪几种？