In the relation MA114-K13: The number of pencils sold varies directly as cost, which of the following statements correctly represents this variation?
a) The number of pencils sold is inversely proportional to cost.
b) The number of pencils sold is directly proportional to the square of cost.
c) The number of pencils sold is directly proportional to cost.
d) The number of pencils sold is inversely proportional to the square root of cost.