How many countries are there ending in 'stan'?

four
seven
twelve
fifteen

One of the main reasons societies settled along rivers in the neolithic era was because a) the village elders demanded it. b) the land there was more valuable. c) it was more safe and secure there. d) it provided irrigation for farming.

As water is cooled from 4 c to 0 c its density

List 3 factors commonly used to select the location of a city