The other-things-constant assumption:

A) allows the economist to make useful predictions.
B) is a prediction.
C) applies only to consumers' decisions and not to those of firms.
D) forces the economist to ignore reality,where things are constantly changing.
E) implies rational self-interest on the part of all economic actors.

The other-things-constant assumption, also known as ceteris paribus, allows the economist to isolate the effect of a single variable on the behavior of economic agents. By holding all else constant, the economist can make useful predictions about how changes in one variable will impact other variables without having to analyze every conceivable factor that may affect behavior. This assumption applies to both consumers and firms and does not imply rational self-interest on the part of economic actors.