You know qu i t e a l o t abou t he l i c op t e r s and
aeroplanes . We l l , do you know how long humans
have been able to use them? The machines that are
able to fly today were developed only during the
last century. This means that a hundred years ago,
there were no aeroplanes or hel i copters l ike the
ones that exi st today. Engineers and technicians
researched for a very long time; they worked for
many years and developed this machinery only a
s ho r t wh i l e ago . L ook , t h i s i s v e r y impo r t an t :
T oday , none o f the mach i ne s that f l y have the
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