Which of the following statements define $$the net defined benefit liability$?$

a$.$ The deficit or surplus, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling

b$.$The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods.

c$.$The present value of any economic benefits available in the form of refunds from the plan or reductions in future contributions to the plan

d$.$The change during the period in the net defined benefit liability that arises from the passage of time