单项选择题：离心泵轴径为30--50mm，转速在1500r/min以下，轴与轴瓦间隙应为（）。

题型：单项选择题

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Apple has entered the textbook market. The tech giantintroduced(推出)

iBooks textbooks many weeks ago. They are digital books in many subjects

taking in science, maths,history and geography. Apple says it offers a “new

textbook experience” and suggests its interactive (互动的) iBooks

textbooks are “the next chapter in learning”.

It sounds like good news for pupils and students. Think of it. No more

carrying heavy backpacks full of textbooks. Every textbook you need can be

stored on your iPad. No more having to buy expensive textbooks which you will only use for a year or two and then sell or give away. Instead of boring

old textbooks which are quickly out of date you can have an interactive

learning experience. You can play videos, examine geometrical（几何）

problems in 3D, listen to music，make notes and mark passages

electronically. You can also share stuff（材料）on social networking sites with your friends.

Of course there’s a catch. You need to own an iPad and as you know,

it is not cheap. You also need to buy digital textbooks, mostly priced each at $14.99 (94.74 yuan) or more. And the rest, will Apple revolutionize(改变)

learning? As they say, is history. That remains to be seen.

1. What is introduced by Apple many weeks ago?

A. iPhone

B.iPad

C. IMAX

D. iBooks

2. If we own iBooks, which of these stasements is Not true?

A. We don’t have to carry heavy backpacks.

B. We can store textbooks on iPad.

C. We still need to buy many expensive textbooks which we will only use for a year or two.

D. We can have an interactive learning experience.

3. What can you do by using iBooks?

A. listen to the songs

B. read and make notes

C. solve maths problems

D. A,B and C

4. What does the underlined sentence “Of course there’s a catch” mean

in Paragraph 3 ?

A. Practice makes perfect

B. It is never too old to learn

C. Every coin has two sides

D. Gold will not buy anything

5. Which is the best title for this passage?

A. The history of book

B. Old text book will be given away

C. Enjoy your iBooks

D. New chapter in learning , real ?

查看答案

离心泵轴径为30--50mm，转速在1500r/min以下，轴与轴瓦间隙应为（）。

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