12．
Move as Millions，Survive as OneGreat white sharks in the Pacific Ocean．Wildebeest in Africa．Arctic terns in the Atlantic．At first，these animals seem completely different．One swims，one walks，and the other flies．But they all have one thing in common．They all migrate．
Some migrating groups move to a place with a better temperature．Some go to find food or wather．The groups travel as one，trying to survive（生存）．During the trip，they face many different challenges．One challenge is distance．Some migrating animals take very long trips．They go far away from their home areas．For example，one great white shark swam from Australia to South African and back．In nine months，it swam about 20，000 kilometers．
Another chanllenge is finding enough food and water during the journey．For example，each Malielephant needs over 200 liters of water each day．To get this，they need to go from one waterhole to another．
In addition，migrating animals have to avoid other animals that want to eat them．For example，the zebra has to stay away from lions．Traveling as a group helps keep them safe．All the zebras in the group can watch for danger．When one zebra is in trouble，the other members make a circle around it．
By working as a group，migrating animals can survive some of the world's most extraordinary journeys．
21．The main idea of the first paragraph is thatCanimals migrate．
A．not all kinds of
B．only similar
C．different kinds of
22．The meaning of the underlined word"migrate"means"B"in Chinese．
A．奔跑
B．迁徙
C．追逐
23．The passage talks aboutBbig challenges for the animals．
A．two
B．three
C．four
24．Which of the following statements is NOT true？A
A．It's about 20，000 kilometers from South Africa to Australia．
B．A Malt elephant needs more than 200 liters of water a day．
C．Zebras help each other when they are in trouble．
25．From the passage，we can infer（推断）thatA．
A．lions may cat zebras
B．lions travel in groups
C．lions try to avoid zebras．
