Answer:
Option D.
Explanation:
In a store cost of CD is $12.
If the cost of CD purchased was graphed on y-axis (output values) and the number of CDs produced on x - axis (input values),
A straight line with positive slope will be graphed because number of the CDs produced will be directly proportional to the cost of CDs.
Line will start from the origin and points lying on it will start from left to right.
Set of points will represent a function.
Therefore, Option D will be the answer.