Read the following passage and mark the letterA, B, C, or D on your answer sheet to indicate the correct answer to each of the questions. Almon Strowger, an American engineer, constructed the fìrst automatic telephone switching system, which had a horizontal, bladelike contact arm, in 1891. The first commercial switchboard based on his invention opened in La Porte, Indiana, a year later ind was an instant success with business users. To access the system, the caller pressed button to reach the desired number and turned the handle to activate the telephone ringer. During the same year, Strowger’s step-by-step call advancement technology was implemented in the long-distance service between New York and Chicago when it proved to have the capacity of carrying signals through cable-joint extensions. The first actual dial telephone, patented by Lee De Forest in 1907, was installed in Milwaukee in 1906. In 1912, their sound transmittal apparatus adapted an electronic tube to tunction as an amplifier. Transatlantic radio-telephone service linked New York and London in 1927. However, the long distances coaxial cable, which was hailed as unprecedented, came on the scene in 1936 connecting New York and Philadelphia. The Bell Laboratories research facility came up with the transistor to replace the cumbersome vacuum tube, thus diminishing the size of the electronic switch system to about 10 percent of that of the original. Crossbar switching, installed in tenminals in 1938, operated on the principle of an electromagnetic force, which rotated horizontal and vertical bars within a rectangular frame and brought contacts together in a split second. A technological breakthroưgh in the form of undersea cables between the United States and Havvaii was implemented almost twenty years later.

Dạng bài Đọc hiểu lớp 12