2. cars. 19 13, the automobile assembly line of Henry Ford, an American automobile manufacturer, officially started, which reduced the cost, improved the efficiency, and made cars enter the homes of ordinary people, becoming a decisive event in this century.
3. the plane. 1901August, 2004 14, the first power plane started flying. ? 1933, the world's first regular air route was opened, which greatly expanded the space for human activities.
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1942 nuclear weapons: the atomic age began at 1942. In order to defeat the Axis fascism, the highest authorities of the United States decided to launch the Manhattan Project aimed at developing atomic weapons. At the end of the year, as part of the Manhattan Project, the first nuclear reactor was built and put into operation under a sports facility of the University of Chicago.
1On July 6th, 945, a mushroom cloud rose from the Atomic Energy Research Center in Los Alamos, New Mexico, USA, and the world's first atomic bomb exploded successfully. On August 6th and 9th of that year, the United States dropped two atomic bombs named "Fat Man" and "Little Boy" in Hiroshima and Nagasaki, Japan. The Japanese emperor then announced his unconditional surrender. The atomic bomb seems to have made great contributions to the victory of World War II, but mankind has lived in the shadow of terrible atomic weapons ever since.
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