migration

definition: 
Seasonal movement of animals from one region to another;Movement of people to a new area or country in order to find work or better living conditions
sentence: 
Seasonal movement of animals from one region to another: This may be an important mechanism promoting the shoreward migration of larval invertebrates and fish. Movement of people to a new area or country in order to find work or better living conditions: The extensive rural-to-urban migration has created a severe housing shortage.
difficulty: 
very easy
toefl frequency: 
3
toefl classification: