四六级考试

【单选题】
A、Light darkens silver salt.
B．Light darkens natural salt.
C．Light darkens silver.
D．Light darkens self-developing film.

网考网参考答案：A
网考网解析：
[听力原文] Today, I’ll be talking about the invention of the camera and photography. The camera is often thought to be an 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 photo graph 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 United States simplified film developing, and Dr. Edwin Land invented the so-called "instant" camera with self-developing film. If we say that taking photograph 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. 17．What discovery was the basis of photography [解析] 推断题。四个选项都是主语相同的选项，因此在听录音的过程中要注意捕捉与主语 (Light)有关的信息。解答此题的关键是注意理解原文中的信息再现。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>