中共十三大的主要贡献是( )。 A．全面阐明了社会主义初级阶段理论 B．明确概括了

Try reading the following sentences as fast as you can. “ She sells seashells by the seashore. The shells she sells are surely seashells. So if she sells shells in the seashore, I’m sure she sells seashore shells.”

Not very easy, was it? What you’ve just read is called a tongue twister（绕口令）. It is an exercise made up of sounds that are hard to pronounce in order to help people pronounce words faster and more correctly. Try the next example.

“Peter Piper picked a peck of picked peppers, Did Peter Piper pick a peck of picked peppers? If Peter Piper picked a peck of picked peppers, where’s the peck of picked peppers Peter picked?”

Tongue twisters usually do not have much meaning. They are just designed to improve people’s ability（能力）to pronounce words. Although they may be very difficult, these exercises are very important to people who are trying to speak English correctly. This is because tongue twisters help people to tell the differences between similar sounds.

So if you wish to pronounce words more smoothly, you’d better try picking out some tongue twisters and practicing them.

小题1:Tongue twisters are helpful in improving ________ skills.

A．listening

B．writing

C．pronunciation

D．communication小题2:The first tongue twister is hard because _________.

A．it is very boring to read

B．it teaches us a lot of knowledge

C．we don’t know who “she” is

D．the sounds of “s” and “sh” are similar小题3:What does the “ability” mean in Paragraph 4?

A．Pronouncing words faster and more correctly.

B．Pronouncing words faster

C．Knowing the meaning of words.

D．Picking out tongue twisters smoothly.

质量为9kg的冰块，密度为0.9×10³kg/m³，

（1）求冰块的体积多大？

（2）若冰吸热后，有30cm³的冰融化成水，求冰熔化成的水的质量．

背压式汽轮机

下列各句中，标点符号使用不正确的一句是

A．本报记者发现一个很有意思的“变化”：希拉克1991年访问西安时，还戴一副宽大的黑边眼镜，后来这副眼镜就再也没在脸上出现过。

B．火箭飞行约25分钟后，星箭分离，卫星进入近地点高度为207公里、远地点高度为35932公里、轨道倾角为28度的地球同步转移轨道。

C．布什表示，他的减税措施刺激美国经济蓬勃发展，“不幸的是民主党仍决心加税，他们若掌控国会，就可以不费吹灰之力办到。”

D．新华网南京1O月28日电(记者石永红、赵丹平、王燕萍)中国唯一地处沿海经济发达地区的长寿之乡——江苏如皋市28日开始举行第三届长寿文化节活动。

无线传输网络中负责数据处理的包括（）。

A.微控制器

B.嵌入式操作系统

C.无线通信协议

D.通信线路