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C) opened the way to a more scientific study of friction
D) has occasionally led to wheel-locking
E) only becomes a problem on poor runways
270- In the passage, it is stated that the braking system of a small aeroplane --------.
A) differs little from that of a larger aeroplane
B) is not very different from that of ordinary road- vehicles
C) cannot be used to control the speed of the aeroplane after landing
D) is specially designed for coping with
high speed landings
E) is both power-operated and manual
The greatest advantage of electrification on railways is that it is both pleasant and efficient.
It brings
the removal of a smoke nuisance from tunnels and from the vicinity of larger cities. Moreover, owing
to
high acceleration, it is possible to provide a more frequent and faster service on densely populated
suburban lines. The track capacity is improved by electrification on mountainous lines because of
increase of speed
both up and down the gradient, generally using electric forms of braking in the
latter case. Some of the major electrification schemes of the world, for example those in Switzerland
and Sweden, have been emerged owing to the desire to operate the railway system without
dependence upon imported fuel.
271- It is pointed out in the passage that the benefits of electric railway reaction ——.
A) cover a cleaner environment and
an improved performance
B) are confined to mountainous areas
C) do not outweigh
the problems involved
D) have only recently become apparent
E) can best be seen in Sweden
272- The author states that on mountainous lines the track capacity is improved by
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