蒸汽往复泵汽缸预热有何作用？

阅读理解。

     Listening test is one of the most important parts of the English exam. Here are some tips (建议) for you.

     Before you start to listen, you need to relax. Don't be stressed out. And try to read the questions. These

questions usually help you understand the conversation or the passage.

      Then listen carefully to the first sentence. It usually tells you the main idea of the passage. When you're

listening, try to do some thinking and take some notes (笔记), such as:

       What happened (发生)? 

       When, where, and how?

       What does the speaker want to tell us?

     In this way, you may understand the passage better.

     Please remember not to think about one or two words for a long time. When you hear some words you

don't know, don't spend too much time on them. Very often, you'll find out what they mean later when you

go on with the listening.

1. This passage mainly talks about _____. [ ]

A. tips on listening

B. tips on speaking

C. tips on reading

D. tips on writing

2. It's better for you to keep _____ when you start to have a listening test. [ ]

A. excited

B. relaxed

C. stressed out

D. worried

3. We should listen to the first sentence carefully, because it usually tells us _____. [ ]

A. the answers to the questions

B. where to write the answers

C. the main idea of the passage

D. how much time left (剩余) for the listening test

4. When you're listening, it's important for you to _____. [ ]

A. remember every word

B. take some notes

C. understand all the words

D. think about one or two words for a long time 

5. The_____ usually help(s) us understand the passage better. [ ]

A. questions

B. first sentence

C. notes

D. A, B and C

（1）用适当的化学用语填空．

名称	2个汞原子	过氧化氢中氧元素的化合价	硫酸铝
化学用语

（2）写出具有下列用途的物质（或其主要成分）的化学式．请从以下物质中选择：

甲烷、食盐、熟石灰、氧气、碳酸氢铵、石灰石、硝酸钾

①“西气东输”工程输送的物质是______；②可用作复合肥料使用的物质是______；

③用于改良酸性土壤的物质是______；④用于日常生活中调味品的物质是______．

局域网在网络拓扑上主要采用了环型、星型和 【6】 结构。

简述《大清新刑律》的特点。

心搏骤停早期诊断最佳指标是（）

A.血压测不到

B.瞳孔突然散大

C.颈动脉和股动脉搏动消失

D.呼吸停止

E.面色苍白和发绀