How do concentration and density relate to distribution of population

The distribution of people across the United States is increasingly dispersed. The total number of people living in the United States is growing slowly - less that 1 percent per year - and the land area is essentially unchanged. But the population distribution is changing from relatively clustered in the Northeast to more evenly dispersed across the country.

Remember, concentration is not the same as density. Two neighborhoods can have the same density of housing but different concentrations. In a dispersed neighborhood each house has a large private yard, whereas in a clustered neighborhood the houses are close together and the open space is shared as a community park.

answer; ///i believe the correct answer is (b) the writing of the ancients who lived in india after the indus valley inhabitants died out;

giant impact theory - the moon was formed from the collision between earth and another mars-sized body.

colliding planetesimals hypothesis - the moon was formed from the same cloud of material as earth.

capture hypothesis - the moon was locked into orbit by earths gravity as it was passing by it.

accretion hypothesis - the moon was formed from collisions and combining of planetesimals.

i think this is right, if not and you know better let me know.