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问题 选择题
近似运算是数学科学的重要分支之一，很多数值都是无理数，我们无法进行下一步运算，因此我们需要取近似值．近似运算方法之一是：构造一个函数f（x），把函数f（x）在x∈[a，b]上的图象近似地看作直线，若a≤c≤b，则f(c)=f(a)+
c-a
b-a
(f(b)-f(a))，若b-a的值越小值越精确．求lg3.5的近似值（　　）（提示：lg2=0.3）
A．0.350B．0.455C．0.501D．0.525
答案

lg3.5≈lg4-

3.5-2
4-2
（lg4-lg2）

=2lg2-0.25×lg2

=1.75×lg2

=1.75×0.3

=0.525．

故选D．

阅读理解

TYPING
This course(课程) is for those who want to learn to type, as well as those who want to improve their typing. The course is not common. You are tested in the first class and begin practicing at one of eight different skill levels(水平). This allows you to learn at your own speed. Each program lasts 20 hours. Bring your own paper.
Course fee(费用): $125        Materials: $25
Two hours each evening for two weeks. New classes begin every two weeks.
This course is taught by a number of professional business education teachers who have successfully taught typing courses before.
 
UNDERSTANDING COMPUTERS
This twelve - hour course is for people who do not know very much about computers, but who need to learn about them. You will learn what computers are, what they can and can't do and how to use them.
Course fee: $75  Jan. 4,7,11,14,18  Wed.& Sat. 9:00-11:30a. m. 
Equipment(设备) fee: $10
David is a professor of Computer Science at Beijing University. He has over twenty years of experience in the computer field.
 
STOP SMOKING
Do you want to stop smoking? Have you already tried to stop and failed? Now is the time to stop smoking using the latest methods(方法). You can stop smoking, and this twelve -hour course will help you do it.
Course fee: $30    Jan. 2,9,16,23     Mon. 2:00-5:00p. m.
Dr John is a practical therapist who has helped hundreds of people stop smoking.
小题1:If you choose the UNDERSTANDING COMPUTERS course, you will have classes_____.
A．from Monday to SundayB．from Monday to Friday
C．on Wednesday and SaturdayD．on Saturday and Sunday
小题2:How long will the STOP SMOKING course last?
A．for a dayB．for three hoursC．for a weekD．for four days
小题3:Mr. Black works every morning and evening, but he wants to take part in one course. What is suitable for him?
A．TYPINGB．UNDERSTANDING COMPUTERSC．STOP SMOKINGD．all courses
小题4:If you want to learn about computers and at the same time you want to improve your typing, how much will you pay for it?
A．$ 75B． $ 150C． $ 115D． $ 235
小题5: What’s the special difference between the TYPING course and the other two?
A．People with different skill levels may learn at different speed
B．You’ll pay less money
C．You will take a test after the course
D．You will pay the fee before practicing
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问答题

有一包白色粉末，可能含有①NaHSO4、②KHCO3、③Ba（NO3）2、④CaCl2、⑤NaNO3、⑥MgSO4

中的一种或几种．实验步骤如下：

①取少量固体投入水中，既有气体又有沉淀产生．

②过滤，取少量滤液加AgNO3溶液，无沉淀产生．

③再取少量滤液，加入足量NaOH溶液，也无沉淀产生．

（1）推断白色粉末中一定有______，一定没有______，不能肯定有没有的是______．（填序号，选错倒扣分，扣完为止，不出现负分．）

（2）请写出实验步骤①中产生气体的离子方程式：______．

（3）请写出实验步骤①中产生沉淀的离子方程式：______．
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