Zee and Co's Operating Profit Increased by 3% Between 20X6

Multiple Choice

Zee and Co's operating profit increased by 3% between 20X6 and 20X7.Which one of the following is NOT a plausible explanation for the increase?

A) Cost of purchases increased, but Zee and Co were able to more than recover the increases in their own selling prices.
B) The interest rate applicable to the business overdraft reduced by 2%.
C) The volume of higher margin sales increased.
D) Zee and Co made substantial savings on operating expenses.