单项选择题

What can we infer from the last paragraph

A．Designing this plane is like a gamble.
B．It's not sure if any manufacturers will invest in this plane.
C．No manufacturers can afford the investment in this plane.
D．The design of this plane is impracticable.

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单项选择题

What can we infer from the saying There's no one thing you can do ( Line 2, Para. 2 )

A．People can do nothing about silencing the noise of airplanes.
B．There are toe many things to be considered when people make planed quiet.
C．People have to deal with everything that causes the noise of airplanes.
D．Only one thing needs to be done when people silence the noise of airplanes.

单项选择题

Which of the following is true according to Paragraph 3

A．The size of the exhaust nozzles is adjustable.
B．The acoustic liners in the exhaust will save fuel.
C．Flaps are devices that brake the airplane.
D．Turbines with three radial-blade fans will reduce non-moving parts.