Scientists workingon a problem do not know and sometimes can't even guess what the final resultwill be.Late on Friday,8 November,1895,Professor Rontgen,a German

physicist,was doingan experiment in his laboratory when he noticed something extraordinary.He hadcovered an electric bulb with black cardboard,and when he switched on

the current he sawlittle dancing lights on his table.Now the bulb was completelycovered;_________(46)?On the table there were some pieces of paper which hadbeen

covered with metalsalts.It was on this paper that the lights were shining. Professor Rontgen tooka piece of this paper and held it at a distance from the lamp.Between it and

the lamp he placed avariety of objects,a book,a pack of cards,a piece of wood and a door key.__________(47).He called his wife into the laboratory and asked her to hold

her hand between thelamp and a photographic plate._________(48),but she held up her hand for aquarter of an hour, and when the plate was developed there was a picture

of the bones of herhand and of the ring on one finger. The mysterious ray could pass through theflesh and not through the bone or the ring.

At a scientificmeeting,Professor Rontegen called this new ray "the unknown" theX-ray. _________(49),and soon there were X-ray machines in all the bighospitals.The

most obvious use forthis discovery was to enable doctors to see exactly how a bone wasfractured._________(50).It was found that these rays could be used to destroycancer

cells,just as theydestroyed the healthy cells of the doctors who first used the machines.Methodswere found later by which ulcers in the stomach could be located,and the

lungs could beX-rayed to show if there was any tuberculosis present._______（47）

A.The ray penetratedevery one of them except the key

B.She was verysurprised by this request

C.how then could anyray penetrate

D.It was a greatinvention

E.Other uses camelater