The idea that tradeoffs have to be made when resources are scarce is reflected in the fact that: points below the production possibilities curve are efficient. points below the production possibilities curve are inefficient. the production possibilities curve has a negative slope. the slope of a linear production possibilities is constant.

The production possibilities curve has a negative slope.

Explanation:

Production possibility frontiers shows us the combination of goods that can be produced in a nation using all of its resources. Since, resources are scarce it is only possible to produce more units of one good by producing less of the other. Thus, the slope of the production possibility frontier is negative.

Other options, does not tell us anything about the scarcity of resources.

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.