A. If there is more lift on one side, the helicopter will flip.
B. Equal lift means that the helicopter will be faster.
C. Dissymmetry of lift makes helicopters fly well.
D. It allows the rotor blade angles to be changed.
B
Đáp án B
Đáp án nằm ở dòng 3, 4 và 5 đoạn 2: “Uneven lift, known as dissymmetry, caused the early helicopters to flip over and confounded the inventors until the creation of the swash-plate; this allowed the rotor blade angles to be changed so that lift would be equal on each side of the shaft.”
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