An ongoing defined benefit plan's future commitments are difficult to estimate for the following reasons except:
A. An unknown percentage of current employees do not work long enough to become "vested" in the plan.
B. An unknown percentage of past employees have not worked long enough to become "vested" in the plan.
C. An unknown percentage of future employees will not work long enough to become "vested" in the plan.
D. An unknown percentage of "vested" employees will retire early.
