President Obama's tweet about being reelected was retweeted by thousands of twitter users within minutes. This is an example of what kind of diffusion? relocation

hierarchical

hearth

contagious

Hierarchical  diffusion

Explanation:

Hierarchical diffusion describes a situation where information is first shared amongst certain people such as a group of connected individuals and then those ones spread it as well to others.

This is what happened here. President Obama's tweet was first seen by people who followed him and so were connected to him on Twitter and then as they retweeted it, more people saw it and retweeted it as well leading to the tweet being shared to millions.

places of higher salinity. there are parts of the ocean where hardly any rain falls but warm dry winds cause lots of evaporation. this evaporation removes water – when water vapour rises into the atmosphere, it leaves the salt behind, so the salinity of the seawater increases. this causes the seawater to become denser.

landlessness of ordinary people

^^something like that^^^