【单选题】If the production possibilities curve is a straight line:
A.
opportunity costs increase as output of either commodity is expanded.
B.
resources are not equally substitutable between the production of the goods.
C.
opportunity costs are negative.
D.
as an increasing quantity of resources are shifted from one manufacturing process (good Y) to another (good X), there is no increase in opportunity cost.
【判断题】If we draw a straight line through the points in a scatter diagram and most of the points fall close to the line, we say that there is a positive linear relationship between the two variables.