Answer:
It´s the radar. It was one of the most useful technological inventions for warfare in the 20th century. Serious development as a military technology began in the 1930s. Radars helped detect enemy air attacks against military targets or bombing raids on cities. It works under the principle of detection of radio waves reflected by metallic objects.
Explanation:
The formation of the North Atlantic treaty organization.
All three of the answers are correct.
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