The graph shows the production of cars per day at a factory during a certain period of time. what is the domain of this function during this period?

graph of days versus cars. points are plotted at the following coordinates: 0 comma 0, 1 comma 50, 2 comma 100, 3 comma 150, 4 comma 200, 5 comma 250, 6 comma 300, 7 comma 350, 8 comma 400, 9 comma 450.

the domain is all real numbers 0 through 9.
the domain is all integers 0 through 9.
the domain is all positive real numbers.
the domain is all positive integers.