单项选择题

Jet belts and rocket belts were developed （）

A．20-30 years ago
B．50 years ago
C．recently
D．30 years ago

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热门试题

单项选择题

An analogy was used to compare the way one could fly in the Solo Flyer to（）

A．how a helicopter flies
B．how the Jetsons fly
C．how the airphibian flies
D．how Superman flies

单项选择题

Which statement is not mentioned in the passage（）

A．Tips are not usually included in the total check.
B．A 15 percent tip in large cities indicates satisfactory service.
C．People tip waiters and waitresses.
D．People always put tips on the tabl