The strong fear of high school math is lost here among the blue light of computer screens and the sounds of typing keyboard．
A fanfare （喇叭声） plays from a speaker as a student passes a chapter test．Nearby another student is watching a video lecture．Another works out a math problem in her notebook before clicking on a multiple-choice answer on her screen．
Their teacher at Agoura High School, US, Russell Stephans, sits at the back of the room, watching as scores pop up in real time on his computer grade sheet．One student has passed a level, the data shows; another is retaking a quiz．
"Whoever thought this up makes life so much easier," Stephans says．
This textbook-free classroom is by no means the norm（常态）, but it may be someday．Slowly, but in increasing numbers, schools across the US are replacing the heavy and expensive textbook with its lighter and cheaper cousin: the digital textbook．
A digital textbook can be downloaded, projected and printed, and can range from simple text to a course filled with multimedia and links to Internet content．Some versions （版本） must be purchased; others are "open source" —free and available online to anyone．
Some praise the technology as a way to save schools' money, replace outdated books and better engage students．Others say most schools don't have the resources to join in, or they question the quality of open-source content．
Paper books still hold the highest percentage of the US textbook market, with digital textbooks making up less than 5 percent, according to analyst Kathy Mickey of Simba Information, a market research group．
But that is changing, as grade schools follow the lead of US universities and schools in other countries, including South Korea and Turkey．
California made the largest embrace （拥抱） of digital textbooks this summer when it approved 10 free high school math and science titles developed by college professors．The state left the choice to use them up to individual schools．
"The textbooks are outdated, as far as I'm concerned, and there's no reason why our schools should have our students pull around these old-fashioned and heavy and expensive books," Governor Arnold Schwarzenegger said this summer．
But some disagree with the idea that digital textbooks will improve education quality．
"Keep in mind that with open-source materials, you have to ask: 'Where are they coming from?'" said Jay Diskey, executive director of the Association of American Publishers' school division．"Is it a trusted source? Is it based on real research?"
Diskey said traditional textbooks offer a comprehensive course, while some open-source texts provide only bits and pieces．"There can be quite a difference of content and accuracy," he said．"In many cases, you get what you pay for．"
The writer's purpose in writing the passage is to  ____    .

A．explain how to use digital textbooks

B．predict the future of paper textbooks

C．describe the current use of digital textbooks and present arguments about it

D．explain the difference between paper textbooks and digital ones

What is Schwarzenegger's opinion of traditional textbooks?

A．He is against getting rid of them．

B．He wants to have them replaced with digital ones．

C．Soon they will no longer be used．

D．He believes that they are to blame for the poor quality of education in California

Diskey holds the view that      .

A．the government shouldn't strengthen the use of open-source digital texts

B．digital textbooks make up for the shortcomings of traditional textbooks．

C．paper textbooks and digital ones both have advantages

D．traditional textbooks have more reliable content

According to the text, which of the following is TRUE?

A．Math is easier with the use of computers．

B．It is believed that digital books will replace traditional ones．

C．Textbook-free classes are the main form of teaching in the US schools．

D．Not all people are in favor of replacing paper textbooks with digital ones．