In September，in Britain，you may see a lot of birds 36 on roofs and telegraph
wires.These birds are swallows.They are 37 together because，very soon，they will
be flying 38 to much warmer lands，where they will find 39 small flying insects on
which they 40 .There are no such insects 4l in Britain during the winter，as it is
42 cold for them.
The swallows settle，fly off，swoop，and 43 again.This they do many times，for they
are making short 44 flights in order to be fit for the long joumey 45 them.
46 of these migrating birds leave Britain in the autumn.They fly 47 for hundreds of
miles 48 they reach the warm lands of Africa.But not all the birds get there，for many of them perish in the stormy weather they meet with 49 .
In the spring of the following year they 50 the long and tiring journey back to Britain.
They return to the identical bam or tree in the 51 district which they had left the 52 autumn.
How do these birds find their 53 there and back over such vast distances?Nobody knows exactly 54 ，but it has something to do 55 winds and air currents.
36.A.being perched
B.perching
C.being perching
D.be perched
37.A.gathering
B.assembling
C.waiting
D.forming
38.A.to south
B.the south
C.to southwards
D.south
39.A.great number of
B.a great deal of
C.plenty of
D.numerous
40.A.feed
B.are fed
C.eat
D.rely
41.A.near
B.about
C.nearby
D.over
42.A.too
B.a bit
C.very
D.much
43.A.fly off
B.swoop
C.settle
D.turn back
44.A.practical
B.practicing
C.practice
D.practised
45.A.in advance
B.ahead of
C.in front of
D.in front
46.A.Swarms
B.Herds
C.Flocks
D.Schools
47.A.firmly
B.stoutly
C.harshly
D.steadily
48.A.until
B.before
C.when
D.as
49.A.in the way
B.on the way
C.half the way
D.all the way
50.A.take
B.fly
C.find
D.make
51.A.old
B.original
C.familiar
D.identical
52.A.before
B.previous
C.ago
D.former
53.A.way
B.path
C.course
D.route
54.A.why
B.when
C.how
D.what
55.A.against
B.away
C.for
D.with
