Part. B

　　Directions: Read the following passage carefully and then give short answers to the five questions.

　　Write your answers on the ANSWER SHEET 2.

　　The construction of extremely bright sources of x-rays has been one of the great – and infrequently told--success stories of science and technology over the past few decades. These facilities, based on evacuated (抽成真空的) , circular tubes several hundred meters in diameter, carry electrons at nearly the speed of light, giving off brilliant bursts of radiation that enable experimenters to examine matter on a scale measured in atoms. Using this extraordinary light, scientists have gained invaluable insights into diverse objects and phenomena, including the structure of molecules, advanced semiconductors and magnetic materials, and the details of complex chemical reactions.

　　Such scientific achievements have been made possible by equally impressive engineering ,advances. Using the brightness of these x-ray sources as a yardstick (测量的尺度) , their rate of improvement since the early 1960s is matched by few other technologies. For example, the increase in computational speed available with the highest-performance computers is often mentioned as an example of the rapid pace of information-age progress. Yet the increase in brightness of the x-ray sources over the same period has occurred far faster.

　　The latest devices, examples of which have come on line over the past five years in various countries, are nearly 100 times brighter than anything built in the previous generation. In fact, these new sources are producing radiation a billion times brighter than that from the sun. Eight of these facilities are now operating, and another two are to begin operating in the near future.

　　Fueling this surge (高潮) in construction of new sources, despite price tags in the range of $100 million to $1 billion per site, is the promise of the most intimate look yet at the structure, composition and chemical bonding of crystals and molecules, in materials ranging from semiconductors to proteins.

　　The astonishing brightness of these devices means that their x-rays come from a source with an extremely small cross-sectional area and that they shine in a very narrow cone ( 圆锥体 ) . The x-rays come from electrons travelling in a bunch with a diameter about the same as that of a human hair.

66. The extremely bright sources of x-rays are based on_________

67. What has this extraordinary light helped scientists do?

68. The new sources of x-rays are producing radiation_________ than that from the sun.

69. All together, there are about_________ new sources operating or to begin operating around the world.

70. What is the size of the bunch of electrons -- the source of X-rays?