有位史学家在评论古希腊城邦的成就时说：“不应看它没能做到什么，而应看它做到了什么

在“探究碰撞中的不变量”的实验中，有质量相等的甲乙两摆球，摆长相同，乙球静止在最低点，拉起甲球释放后与乙球刚好正碰，碰后甲球静止，乙球摆到与甲球初始位置等高。现换为同质量的两个粘性球，重复以上操作，碰后两球粘合在一起运动，则：

A．两次碰撞的整个过程中机械能不可能守恒

B．第一次两球碰撞瞬间的前后，动量守恒，机械能不守恒

C．第二次两球碰撞瞬间的前后，动量守恒，机械能不守恒

D．第一次碰撞中，从甲球开始下落到乙球上升到最高点过程中动量守恒

假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的一下作文。文中共有10出语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。

增加：在缺词处写一个漏字符号（）, 在其下面写上该加的词。

删除：把多余的词用斜线（＼）划掉。

修改：在错的词下划一横线, 在该词下面写上修改后的词。

注意：

1. 每处错误及其修改均仅限一词；

2. 只允许修改10处, 多者（从第11处起）不计分。

Last Saturday I went to the library as usually. At about noon, I was enjoying my reading near a lake while suddenly I hear someone crying for help. I went up to see what was happened. I was shocking to find a little child struggling in the water in the distance while many peoples were standing by without doing anything. Without any hesitation, I had pushed through the crowd as I took off my coat, but jumped into the water quickly. I managed to reach him and carried him back to safety. To his great relief, the kid was saved.

I was proud what I had done. I hope everyone can give a hand when someone else is in need.

流转税类不包括。

A、营业税

B、增值税

C、消费税

D、房产税

上海世博会的主题：“城市，让生活更美好。”下列哪项是城市生态系统的特点  [ ]

A．以农作物为主体，动植物种类相对较少   

B．消费者主要是人类，植物的种类和数量少   

C．动植物种类繁多，有“绿色水库”之称   

D．缺乏高大植物，降雨量很少

宇宙中最基本的天体类型是（）

A.恒星和行星

B.恒星和星云

C.彗星和地球

D.卫星和星云