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【单选题】
Aircraft lighter than air lifts off by ____.
A.
Static buoyancy generated by air
B.
Aerodynamics
C.
Hot air
D.
Helium
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参考答案：
参考解析：
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【多选题】Main differences between balloon and airship are ____.
A.
Configuration
B.
Motive power
C.
Direction Control
D.
Filling gases
【单选题】The main difference between rotorcraft and helicopter is that ____.
A.
They have different fuselages
B.
They have different rotor
C.
They have different way to drive the rotor
D.
If their rotor can generate lift or not
【多选题】The advantages tiltrotor aircraft have over helicopter are ____.
A.
Longer flight range
B.
Lower cost
C.
Simpler structure
D.
Higher speed