5Whenever a defined-benefit plan is amended and credit is given to employees for years of service provided before the date of amendment

the expense should be recognized immediately, but the liability may be deferred until a reasonable basis for its determination has been identified.

both the accumulated benefit obligation and the projected benefit obligation are usually less than before.

the expense and the liability should be recognized at the time of the plan change.

both the accumulated benefit obligation and the projected benefit obligation are usually greater than before.

6,Prior service cost is amortized on a

straight-line basis over the expected future years of service.

years-of-service method or on a straight-line basis over the average remaining service life of active employees.

straight-line basis over the average remaining service life of active employees or 15 years, whichever is longer.

straight-line basis over 15 years.