In September, in Britain, you may see a
lot of birds{{U}} (36) {{/U}}on roofs and telegraph wires. These birds
are swallows. They are{{U}} (37) {{/U}}together because, very soon, they
will be flying{{U}} (38) {{/U}}to much warmer lands, where they will
find{{U}} (39) {{/U}}small flying insects on which they{{U}} (40)
{{/U}}. There are no such insects{{U}} (41) {{/U}}in Britain during
the winter, as it is{{U}} (42) {{/U}}cold for them. The
swallows settle, fly off, swoop, and{{U}} (43) {{/U}}again. This they do
many times, for they are making short{{U}} (44) {{/U}}flights in order
to be fit for the long journey{{U}} (45) {{/U}}them. {{U}}
(46) {{/U}}of these migrating birds leave Britain in the autumn. They
fly{{U}} (47) {{/U}}for hundreds of miles{{U}} (48) {{/U}}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{{U}} (49) {{/U}}.
In the spring of the following year they{{U}} (50)
{{/U}}the long and tiring journey back to Britain. They return to the
identical barn or tree in the{{U}} (51) {{/U}}district which they had
left the{{U}} (52) {{/U}}autumn. How do these birds find their{{U}}
(53) {{/U}}there and back over such vast distances? Nobody knows
exactly{{U}} (54) {{/U}}, but it has something to do{{U}} (55)
{{/U}}winds and air currents.
【正确答案】
B
【答案解析】[解析] 本句意为：你可以看见很多鸟儿在屋顶或电线上栖息。 see sb. doing sth. 看见某人正在干某事。