A. It was the first practical helicopter flight
B. It lasted 7 minutes and 40 seconds
C. It was the first time a helicopter lifted into the air without ground assistance
D. It was the first time a helicopter lifted into the air
C
Đáp án C
Đáp án nằm ở dòng 1 + 2 đoạn 3: “On November 13, 1907, the French pioneer Paul Cornu made history by lifting a twin-rotor helicopter into the air for a few seconds without ground assistance”
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