下列对于生物体结构和功能的说法,正确的是 ①RNA与DNA都是由四种核苷酸组成,

题型:选择题

问题:

下列对于生物体结构和功能的说法,正确的是

①RNA与DNA都是由四种核苷酸组成,可以储存遗传信息 ②核孔是生物大分子物质进出的通道,它对物质的通过没有选择性 ③ATP脱去2个磷酸基团后是RNA的基本组成单位之一 ④卵细胞体积较大有利于和周围环境进行物质交换,为胚胎早期发育提供所需养料[ ]

A.①②

B.②④

C.③④

D.①③

考点:核酸的组成和功能细胞核的结构ATP的结构实验:细胞大小与物质运输的关系
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已知有理数a,b,c,d满足a3-2005=b3+2027=c3-2822=d3+2820,那么(  )
A.a>c>b>dB.b>d>a>cC.c>a>b>dD.d>b>a>c
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埃及最早的文字实际上是象形文字,由(),表音符号和()组成.

题型:选择题

阅读理解。

     It is Saturday afternoon. You and your friends are planning to go to the movies and then spend the night

together. Just as you start to get ready, your dad reminds you that it is your aunt's birthday and the whole

family is going out to dinner to celebrate. How can this possibly end without a huge argument?   

     One of the greatest sources of tension (紧张情绪) between teenagers and their families is the struggle

to balance personal desires with family expectations. As you are getting older, you are becoming more

independent and more interested in being with your friends.   

     However, at the same time, your family is trying to figure out how to deal with these changes. While

you once spent most of your free time with your family, you are now often absent from home. Parents

may get their feelings hurt. Or they might feel that they are losing control of their family during this period.

You might feel angry that so many family demands are placed on you.   

     There are a few things you can try to make it a little easier to ease (缓解) the tension.   

     * Make your plans in advance. Ask your parents if there is anything else planned at that time.   

     * When something with your friends interferes (冲突) with a family event,try to figure out if there is

any way you can do both.   

     * Suggest something you would really like to do with your family. Sometimes parents feel better just

knowing their teenager wants to spend time with them.   

      Some of the time you won't be happy with the outcome (结果). You might either have to disappoint

your parents or have to miss out being with your friends. However, if you show consideration for the

feelings of both your family and your friends,you can solve the problem in a tender way.

1. The purpose of the first paragraph is to _____. [ ]

A. show a disagreement of views

B. serve as a description of teenager trouble   

C. serve as an introduction to the discussion

D. show the popularity of teenager problem

2. The tension between teenagers and their families is caused by the fact that _____. [ ]

A. teenagers don't like to take family demands   

B. parents want to keep their family under control   

C. parents feel unhappy that their children make so many friends   

D. both parents and teenagers don't pay attention to each other's feeling much

3. What's the purpose of the passage? [ ]

A. To inform us of parent and teenager tension.

B. To advise teenagers how to deal with their tension with their families.

C. To persuade parents to show consideration for teenagers.

D. To tell us about a common teenager problem.

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( )是佝偻病患者常见步态。

A.剪刀步
B.醉汉步
C.跨阈步
D.鸭步

题型:选择题

电磁流量计对安装环境的要求?

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