Answer: B. Decrease
Step-by-step explanation:
Return on investment refers to the ratio between the net income and investment. It should be noted that a high return on investment implies that the investment's gains compare favourably to the cost.
In this scenario, since a large amount of raw material was bought in advance and stored in the manufacturing plant inventory, this will lead to an increase in the cost of production which therefore will reduce the return in investment.
Therefore, the correct option is B.