Great white sharks in the Pacific Ocean. Wildebeest in Africa. Arctic terns in the Atlantic. At first, these animals seem 【小题1】 (complete) different. One swims, one walks, and the other flies. But they all have one thing 【小题2】 common. They all migrate.

Some migrating animals move to a place 【小题3】 has a better temperature. Some go to find food or water. The groups travel as one, trying to survive. During the trip, they face 【小题4】 (many) challenges than we can imagine.

One challenge is distance (距离). Some migrating animals take very long trips. They go far away from 【小题5】 (they) home areas. For example, one great white shark swam from Australia to South Africa and back. In nine months, it swam about 20,000 kilometers.

Another challenge is finding enough food and water during the journey. For example, each Mali elephant needs more 【小题6】 200 liters (公升) of water each day. To get this, they need 【小题7】 (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 【小题8】 (help) 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 【小题9】 (work) as a group, migrating animals can survive some of the world’s most 【小题10】 (wonder) journeys.

A recent study found that extreme environmental change could cause an “extinction domino effect.”【小题1】it may seem unimportant if we lose one rat species, it matters because all species【小题2】(connect ) through their interactions in a web of life. A balanced ecosystem is one in which each species plays an important role and relies on the services provided by other species【小题3】(survive). Healthy ecosystems are more productive and resistant to disruptions.

Wild elephants that had been roaming the southern Chinese province of Yunnan for more than three months returned to a “more appropriate” habitat, Chinese experts told Xinhua news agency.

The animals began a migration in May 【小题1】 their usual habitat in Xishuangbanna, 【小题2】 region known for its tropical forest, to the north of the province without clear reason. The herd managed 【小题3】 (cross) the Yuanjiang River Sunday, the main obstacle they had to continue their return to a more favorable habitat. The 【小题4】 (arrive) of the rainy season in the area in July added difficulty to 【小题5】 (it) crossing, since the river flow has increased 【小题6】 (considerable). According to Xinhua, authorities blocked the river bank with dozens of trucks to prevent the elephants from crossing, 【小题7】(force) them to continue their journey to a bridge, through 【小题8】 they could cross the river without complications. Chen Mingyong, an elephant researcher at Yunnan University, said the Yuanjiang River is the dividing line that marks “the suitability of the environment for the life of elephants”. In the north, the original direction the animals took, it is colder and there is less food, 【小题9】 the Yuanjiang River basin, where they are found, has plenty of food.

According to Chen, elephant habitats 【小题10】 (divide) into four categories: “highly appropriate, appropriate, normal and inappropriate,” and the animals are now in a suitable one.