B

      In science fiction TV programs such as Star Trek , tractor beams (光线) are used to draw   spaceships and move objects  For years, scientists have labored to reproduce this feat（技艺）.  In 2013. they succeeded  A team of British and Czech scientists, led by Dr Tomas Cizmar. say  they have created a rea-life "tractor beam". like the kind from Star Trek . which uses a line of  light to attract objects. at least at a microscopic level

      Light control techniques have existed since the l970s. but this is thought to be the first  time a beam has been used to draw objects towards a light source  Usually when microscopic  objects are hit by a line of light. they are forced along the direction of the beam  After many  years' research. Dr Cizmar's team discovered a technique that allows for the radiant force(辐射力) of light to be changed and to use the negative force to draw out certain particles（小颗粒）

 Dr Cizmar says that even though it is a few years away from practical use. the technology　 has huge potential for medical research  In particular. the tractor beam is highly selective in　 the particles it can attract. so it can pick up particles that have specific characteristics. such as　 size or composition. in a mixture  "Eventually, this could be used to separate white blood　cells. for example," Dr Cizmar told BBC News

      It has been a primary plot design in science fiction TV programs and movies to allow ob-

jects like spaceships to be trapped in a line of light But Dr Cizmar said this particular technique would not eventually lead to that A transfer of energy happens in the process  On a microscopic level that is OK. but on a large level it would cause huge problems  A large object　could be destroyed by the heating, which results from the massive amount of energy necessary to pull it.

24. What is this passage mainly about?

     A The application of light control techniques in modem society.

     B The uses and limitations of a scientific invention by a research team

     C. The adoption of light control techniques in medical treatment.

     D. The influences and effects of scientific developments on science fiction

25. Which of the following is TRUE about Dr Cizmar's tractor beam?

     A It moves big objects as the tractor beam did in Star Trek.

     B It is the first beam that pushes objects forward

     C. It relies on negative force to pull out specific kinds of particles.

     D. It is currently being used for separating blood cells in medical research

26. What does "that" in the last paragraph refer to?

     A Transferring a massive amount of energy.

      B. Making science fiction programs and movies.

     C. Burning a large object into ashes.

      D. Catching spaceships in a beam of light

27. What is the tone of this passage?

     A Objective        B. Suspicious        C. Admiring.        D. Pessimistic.
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