What is the by-pass ratio in a turbofan?

In an turbojet, combustion chamber's function is:

Which of the following statements is true?

1 A turboprop needs a gearbox to reduce the rotation speed of the propeller with respect to the turbine

2 If oil prices continue rising, we will probably see more turboprop aircrafts

3 Turboprops are more efficient than turbofans at lower speeds

Which of the following statements is true? 

1 The speed of the air intake to the compressor must not exceed Mach 0.5 

2 The Thrust of a turbojet is obtained thanks to the high acceleration of the exhaust gases at the nozzle

3 In an adapted nozzle, the pressure of the gases at the nozzle is equal to the atmospheric pressure, being the thrust maximum

About piston engines and gas turbines,

1 A piston engine is a volumetric machine

2 A piston engine can develop more specific power than a turbine

3 A gas turbine is a flow machine

Which of the following statements is true?

1 Centrifugal compressors are more suitable to be used on large airliners (A380, B747, B777,...)

2 Centrifugal compressors are more expensive than axial compressors

3 Axial compressors are more resistant to the entry of objects and particles than centrifugal compressors 

Which of the statements below is true...

1 thanks to the design of the diffuser, the power of a turbojet does not depend so strongly on the altitude as a piston engine.

2 the power of the turbojet is basically controlled through the gas throttle

3 during take-off, almost all the power provided by the turbojet is used

Which of the following statements is true?

1 thrust reverse are used at the landing to stop the plane

2 the vectorized drive helps increase the manoeuvrability of an aircraft

3 after-burners increase engine efficiency

An aircraft is at the runway is preparing to take off. We can assure that:

We will get the maximum propulsive efficiency when...