The phrase "invisible hand" means that:

no one person or firm actually sets the price.

The tendency of competition to cause individuals and firms to unintentionally promote the interests of society.

market prices are not always known to buyers and sellers.

buyers and sellers often do not meet so the transactions are invisible.

The correct answer is letter "B": The tendency of competition to cause individuals and firms to unintentionally promote the interests of society.

Explanation:

In his book "An Inquiry into the Nature and Causes of the Wealth of Nations" (1776), British economist Adam Smith (1723-1790) introduced the term "invisible hand" to refer that economic factors (buyers and sellers) naturally influence in the fluctuations of supply and demand without the need for the intervention of the government.  

According to Smith, buyers and sellers interactions act as an "invisible hand" arranging proper levels of competition between businesses and promoting the best interest of societies.

answer: a. the kind of population living in your neighbourhood.

the census explorer data tool by the us census bureau allows the user to zoom in on any neighbourhood within the united states and find the kind of people residing in that by race and age.  

the tool needs to needs to be used twice – once in order to find what type of people reside in a neighbourhood, and then to see the age groups of the people in the same neighbourhood.

answer; empowerment and collaboration;