What do astronomers mean when they refer to "gaps" in the asteroid belt between mars and jupiter?

Which summarizes the relationship between density of an element and its distribution in earth? a. the greater an element’s density, the greater the amount of it found in the crust. b. the denser an elements is, the smaller the amount of it earth core. c. the greater an elements density, the smaller the amount of it’s found in the crust

Where does the availability of water pose the greatest problem

Plz asap can someone find the answer or the mark scheme or anything plzzz you : ) ‘it's perfectly understandable that hundreds of millions of people around the world live close to volcanoes’ use evidence to support this statement. (6 marks)