1957 AHSME Problem 16

Goldfish are sold at 15 cents each. The rectangular coordinate graph showing the cost of 1 to 12 goldfish is:

\begin{array}{l} \textbf{(A)}\ \text{a straight line segment} \qquad \\ \textbf{(B)}\ \text{a set of horizontal parallel line segments}\qquad\\ \textbf{(C)}\ \text{a set of vertical parallel line segments}\qquad\\ \textbf{(D)}\ \text{a finite set of distinct points} \qquad\textbf{(E)}\ \text{a straight line} \end{array}

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.