Option C is the correct option.
Explanation:
When two comparable items are given, and both have different units, it cannot be compared. We should always convert both the units in one unit, if we want to compare the two items. This can be done by converting 1st item's unit in second one or vice versa. Hence, option C is the correct answer.
C - Use conversion rates to change one unit into the other unit, so that both prices are listed using like units.