听力原文: Today, I'll be talking about the invention of the camera and photography. The camera is often thought to be a modem invention. But as early as 1727, a German physicist discovered that light darkens silver salt, a chemical compound. Using as a camera, a big box with small hole to let the light in, he made temporary images on the salt. Silver salt is still the base of film today.
Then a French scientist made the first permanent picture by using a special piece of metal sensitized with silver salt. A photograph he made in 1826 still exists. The painter, Daguerre improved on the process by placing common salt on the metal, This was in 1839, the official date of the beginning of photography, but the problem was the printing of the photographs, and it wasn't until other scientists developed the kind of paper we now use, that good printing was possible and photograph became truly modern.
In 1860's, Matthew Bradey was able to take his famous pictures of the American Civil War. In the 20th century, George Eastman of the Untied States simplified film developing, and Dr. Edwin Land invented the so-called "instant" camera with self-developing film. If we say that photography came into existence in 1839 it follows that it has taken more than one hundred years for the camera to reach its present condition of technical refinement.
(30)
A.Light darkens silver salt.
B.Light darkens natural salt.
C.Light darkens silver.
D.Light darkens self-developing film.
第4题
气体燃料主要有()、液化石油气、发生炉煤气和焦炉煤气。
A.甲烷
B.二氧化碳
C.天然气
D.氧气
第6题
2003年到2007年,消费量持续上升的生活能源是()。
A.煤炭
B.煤油
C.液化石油气
D.热力
第8题
液化石油气常用的制取方法有()。
A.煤加氢
B.在炼油厂回收液化石油气
C.催化裂化
D.人工合成
第9题
下列介质中,()是可燃液体。
A.液化石油气
B.35号轻柴油
C.原油
D.甘油
E.汽油
F.重柴油
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