50 1)it has liquor water and a (protect) atmosphere, both of which are essential for life. 2)and of all the planets in solar system, the earth is at just the right (distant) from the sun to be neither too hot nor too cold 3)earth's interior consists of (lay) of rock that surrounds a core made of iron and nickel. 4)however, many people are worried that (pollute), human overpopulation, and (use) of resources may destroy this balance and make the (safe) for plants and animals
2-distance
3-layers
4-pollution,useful,unsafe