离心泵是靠离心力来工作的，启动前泵内（）是它的必要条件。

Your computer has been playing music for years, one CD at a time. Now hundreds of songs can be stored in your PC if they' re in the MP3 format (格式).

What is it? MP3 compressed(压缩) music into small computer files. You may download MP3 music several ways: Music can be downloaded from websites that have turned wide music libraries into MP3. Once MP3 music is on your PC’s hard drive, you can play it through your computer's speakers, "burn" it onto blank CDs or swap(交换) MP3 files with friends using e -mail.

How much? Software needed to play and convert MP3 music is often free. Compact portable MP3 players start at around $ 40 and can hold hundreds of songs. A blank CD on which you can record music costs about a dollar.

Advantages MP3 turns your home PC into a jukebox(自动唱机) . Small MP3 players are the size of a deck of cards(一副牌), making it easy to take hundreds of songs with you.  Disadvantages You may find that some websites only allow you to listen but you can't download music. Others let you download music but can't be copied to MP3 players. And a growing number of new CDs make it impossible to copy songs to a computer.

小题1:How can you get MP3 music?

A．By turning your home PC into a jukebox.

B．By taking your own music or songs with you.

C．By copying songs to a PC through the speakers.

D．By downloading from websites, which have turned music libraries into MP3.

小题2:What is the closest meaning of the underlined word "burn"?

A．Copy.

B．Play.

C．Store.

D．Change.

小题3:Which is NOT true according to the passage?

A．MP3 music is often free.

B．MP3 music can be "burned" onto blank CDs or be swapped with friends by e -mail.

C．MP3 music can be taken along while traveling.

D．A growing number of new CDs make it possible to copy songs to a computer.

小题4:How much will you pay for a compact portable MP3 player?

A．Free.	B．At least 10 dollars.
C．About forty dollars.	D．About a dollar.

小题5:How many disadvantages of MP3 can we see from the passage?

A．2

B．3

C．4

D．5