Which linear graph represents a proportional relationship?

A graph of a straight line that passes through the points 0 comma 1 and 3 comma 0.
A graph of a straight line that passes through the points 0 comma 0 and 1 comma 2.
A graph of a straight line that passes through the points 0 comma negative 4 and 1 comma negative 4.
A graph of a straight line that passes through the points 1 comma 0 and 1 comma 1.

The correct answer is:

A graph of a straight line that passes through the points 0 comma 1 and 3 comma 0.