Answer:
C
Explanation:
C is the most logical explanation given. The other answers may be true, but option C would strengthen the manager's rationale most. It is assumed that the number of cola drinks would be a similar number to the iced-tea beverages. Therefore, if there is less iced-tea beverages in the cooler at the end of the day, then it is logical to assume that more iced-tea beverages were consumed throughout the day.
This would lead the manager to believe that iced-tea is more popular than the cola beverages, and hence, he would need to buy more iced-tea drinks than cola.