B is corrent. The projected benefit obligation is the present value of pension benefits accrued to date using assumptions as to future compensation levels.
A is incorrect because the accumulated benefit obligation is the present value of pension benefits accrued to date based on present salary levels.
C is incorrect because accrued pension cost is the balance sheet liability resulting when pension expense recognized exceeds pension funding.
D is incorrect because prior service cost is the increase in projected benefit obligation resulting from a pension plan amendment.
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