Today's class, Mr. Schick helped us to reviewed some words we mentioned before. Life expectancy: in a country or an area, the average age of people they can live. Crude birth rate: the number of born in per 1000 people in the same year. Crude death rate: the number of death in per 1000 people in the same year. Developed country: means country which has already developed well. Developing country: means country which is still developing. Rate of nature increase: The difference between crude birth rate and crude death rate. Immigration: number of people who come into the country. Emigration: number of people who leave the country. Net migration rate: number of people who come or leave a country in a year.