由于肩关节属于较大的关节，其结构稳定故一般不容易脱位。

给下面一则消息加上标题。（5分）

今天11时至12 时，国家游泳中心“水立方”“穿”上最后一块膜“外衣”― 最后一片“ETFE ”膜被安装在“水立方”的“屋顶”。被蓝色“水泡”包裹的“冰块”建筑外观首次全景亮相。北京电视台新闻中心通过安装在现场的6 台摄像机从6 个角度全程直播了这一历史时刻。在2008 年奥运会开幕倒计时的591 天，作为北京奥运三大标志建筑之一的“水立方”已经展示出完整的“奥运装”，转入内部设备安装和装修阶段。预计整个工程将于2007 年10 月全部完工。

（18分）如图在xoy平面内有平行于x轴的两个足够大的荧光屏M、N，它们的位置分别满足y=l和y=0，两屏之间为真空区域。在坐标原点O有一放射源不断沿y轴正方向向真空区域内发射带电粒子，已知带电粒子有两种。为探索两种粒子的具体情况，我们可以在真空区域内控制一个匀强电场和一个匀强磁场，电场的场强为E，方向与x轴平行，磁场的磁感应强度为B，方向垂直于xoy平面。

试验结果如下：如果让电场和磁场同时存在，我们发现粒子束完全没有偏转，仅在M屏上有一个亮点，其位置在S（ 0 , l ）；如果只让磁场存在，我们发现仅在N屏上出现了两个亮点，位置分别为P（ -2l ， 0 ）、Q（ ，0 ），由此我们可以将两种粒子分别叫做P粒子和Q粒子。已知粒子间的相互作用和粒子重力可以忽略不计，试求（坐标结果只能用l表达）：

（1）如果只让磁场存在，但将磁场的磁感应强度减为B₁= ，请计算荧光屏上出现的所有亮点的位置坐标；

（2）如果只让电场存在，请计算荧光屏上出现的所有亮点的位置坐标；

（3）如果只让磁场存在，当将磁场的磁感应强度变为B₂= kB时，两种粒子在磁场中运动的时间相等，求k的数值。

阅读理解。

     Parents should stop blaming themselves because there's not a lot they can do about it. I mean the teenager

problem. Whatever you do or however you choose to deal with it, at certain times a wonderful, reasonable and

helpful child will turn into a terrible animal.

     I've seen friends deal with it in all kinds of different ways. One strict mother insisted that her son, right

from a child, should stand up whenever anyone entered the room, open doors and shake hands like a gentleman.

I saw him last week when I called round. Sprawling himself (懒散地躺) on the sofa in full length, he made no

attempt to turn off the loud TV he was watching as I walked in, and his greeting was no more than a quick

glance at me. His mother was ashamed. "I don't know what to do with him these days," she said.

     "He's forgotten all the manners we taught him." He hasn't forgotten them. He's just decided that he's not

going to use them. She confessed (坦白) that she would like to come up behind him and throw him down from

the sofa onto the floor.

     Another good friend of mine let her two daughters climb all over the furniture, reach across the table, stare

at me and say, "I don't like your dress; it's ugly." One of the daughters has recently been driven out of school.

The other has left home.

     "Where did we go wrong?" their parents are now very sad. Probably no one is to blame on this issue.

1. This text is most probably written by _____.

A. a specialist in teenager studies

B. a headmaster of a middle school

C. a parent with teenage children

D. a doctor for mental health problems

2. The underlined word "it" in the second paragraph refers to _____.

A. the change from good to bad that's seen in a child

B. the way that parents often blame themselves

C. the opinion that a child has of his parents

D. the advice that parents want their children to follow

3. From the second example we can infer that the parents of the two daughters _____.

A. pay no attention to them

B. are too busy to look after them

C. have come to hate them

D. feel helpless to do much about them

4. What is the writer's opinion about the sudden change in teenage children?

A. Parents have no choice but to try to accept it.

B. Parents should pay still more attention to the change.

C. Parents should work more closely with school teachers.

D. Parents are at fault for the change in their children.

下列叙述中与盐酸美沙酮相符的是

A．结构式中含有二甲氨基

B．其水溶液不稳定，光照下变色

C．分子中不含手性碳原子

D．镇痛效果低于吗啡和哌替啶

E．体内代谢产物仍有镇痛作用

在焊接过程中，由于某种原因，导至焊接火焰从焊枪向乙炔及乙炔发生器回串的现象叫（）

A.回火

B.退火

C.正火