Answer: 1920- Hair Dryer
1920- First radio station
1920- The Thompson Sub-Machine Gun
1920- The Band Aid
1921- First robot built
1923- Traffic Signal
1925- Mechanical Television
1926- Liquid Fueled Rockets
1928- Penicillin
1929- Car radio
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Explanation:
The answer is a I hope that helps
Narrow specialization of tasks within a production process so that each worker can become a specialist in doing one thing, especially on an assembly line. In traditional industries (see sunset industries), division of labor is a major motive force for economic-growth. However, in the era of mass customization (which requires multiple skills and very short machine change-over time), division of labor has become much more flexible. Also called specialization of labor.
Because, the Persians felt that their army could outnumber Greece, also because they might not have known what they were getting into when they attacked the Greek city-states. Hope that helped :D