One Component of Net Pension Expense,unrecognized Gains and Losses,comes from Which

Multiple Choice

One component of net pension expense,unrecognized gains and losses,comes from which of the following sources?

A) Difference between expected and actual prior service and transition costs only
B) Difference between expected and actual return on plan assets only
C) Projected benefit obligation changes due to changes in pension assumptions only
D) Projected benefit obligation changes due to changes in pension assumptions only,and the difference between expected and actual return on plan assets