The Following Graph Shows the Populations of the Metropolitan Areas

Multiple Choice

The following graph shows the populations of the metropolitan areas of City X and City Y over six years.
-If equations of the form y = f(t) were determined that modeled either of the two graphs, then the variable t would represent _______ and the variable y would represent _______.

A) population (in millions) ; year
B) City Y; City X
C) City X; City Y
D) year; population (in millions)