It was a dark November day in 1895. In a laboratory at the royal University of Wurzburg, in western Germany, a 50-year-old physics professor, Wilhelm Roentgen, performed what looked like a type of magic. He placed a glass vacuum（真空）tube inside a black cardboard box and applied a high-voltage current（高压电流）. He suddenly noticed that, on a bench nearby, a piece of paper coated with a chemical substance began giving off an strange light. Over the following two weeks, Roentgen performed a series of experiments that proved the existence of a form of electro-magnetic（电磁的）radiation he called X-rays.

His astonishing discovery has led to a deeper understanding of the physical world----in particular, to the field of medical diagnosis（诊断）.

X-rays are widely used in medicine to make radiographs or X-rays pictures of the bones and internal organs of the body to see whether diseases exist, such as broken bones or lung diseases.

A radiograph is made by passing an X-rays beam through a patient’s body onto a piece of photographic film. The bones takes in more of the rays than do muscles or other organs, so the bones throw the sharpest shadows on the film.

Improvements over the past century----from fluoroscopy（荧光透视法）to CT scans---- have made X-rays technology an invaluable tool of medicine.

78. At the beginning of the passage, Prof. Wilhelm Roentgen was _______.

A. performing an entertaining program                            B. playing magic

C. doing some experiments                                            D. None of above

79. When Prof. Roentgen placed a glass vacuum tube in a black box and applied a high-voltage current, he _______.

A. saw a bench nearby

B. noticed a piece of paper on a nearby bench begin to burn slowly

C. noticed a piece of paper on a nearby bench begin to give out strange light

D. noticed a piece of paper was coated with a chemical substance

80. The bones have clearer shadow on the photographic film than do muscles or other organs, because ______.

A. the bones are harder than them

B. the bones can help absorb more rays than them

C. the bones can block more rays than them

D. X-rays cannot pass through the bones