【单选题】Formation flight is more comfortable because passengers can not see the other planes.
【简答题】A.We can do without railways. B.Trains have much in common with motorcars and planes. C.Motorcars and planes are not as good as trains. D.Trains are as good as motorcars and planes.
【单选题】there is ( )words in this passenge.
【单选题】A camera lens is preferable to a pinhole because it can ______ .
A.
offer a choice of planes of focus
B.
gather more light rays
C.
control the size of the image formed on the film
D.
gather more light rays and bring them to a focus at a given plane