Which linear graph represents a proportional relationship?
a A graph of a straight line that passes through the points 0 comma 1 and 3 comma 0.
b A graph of a straight line that passes through the points 0 comma 0 and 1 comma 2.
c A graph of a straight line that passes through the points 0 comma negative 4 and 1 comma negative 4.
d A graph of a straight line that passes through the points 1 comma 0 and 1 comma 1.