阅读理解
Thomas Edison received a patent(专利) for his kinetoscope(电影放映机) on August31, 1887. It was a machine for viewing moving pictures. Edison had hoped to combine his no invention with the phonograph(留声机), which he had invented 10 years earlier. He thought that people would like to watch moving pictures that went along with the sound. He was not able to make them work together. The kinetoscope, however, was a popular attraction by itself. A person looked through small holes in a box-like machine and saw pictures in action. One of the first films made showed a man sneezing.
A problem with this invention was that only one person could view the moving pictures at a time. By 1891, Edison had invented a projector that showed the film on a screen. Many people could watch together.
In 1893, Edison built a motion-picture studio. He made over 300 silent films. Most of them were short. That was because the pictures flashed, or shook a lot. It was hard for people to watch more than 10 minutes at a time.
The first films were mostly of real events. They would show famous people walking somewhere, cars on a street, burning houses, and other news stories. Then comedies and short dramas were made.
Edison's movie studio closed in 1918. By then other companies were also making films. Better cameras were made. Sound was added. Then color came along. Today, movies are among the most popular forms of entertainment.
是理想电压表．现将负载电阻的阻值减小为R=5R0，保持变压器输入电流不变，此时电压表的读数为5.0V，则（ ）