For a business that operates above breakeven and experiences a 15% increase in sales: Which of the following statements will NOT be true as a direct consequence of increasing sales volume 15% above the present level (all the other variables remain constant)?

a) the total marginal contribution will increase by 15%

b. Operating income (OI) will increase by 15% over the current OI (operating income)

c. the ratio of variable costs to sales remains constant

d. total variable costs will increase by 15%