Choice "D" is correct. The four main components of other comprehensive income include:

• Pension changes in funded status: due to gains/losses, prior service costs, and net transition assets or obligations.

• Unrealized gains and losses: unrealized holding gains/losses on available for sale securities and unrealized holding gains and losses on debt securities transferred from the held to maturity to available for sale classification.

• Foreign currency items, including translation adjustments.

• The effective portion of cash flow hedges.

Choice "a" is incorrect. Unrealized gains/losses on trading securities go on the income statement.
Choice "c" is incorrect. A transfer from the available for sale category to the held to maturity classification would be a move out of other comprehensive income.
Choice "b" is incorrect. The difference between the fair value of plan assets and the accumulated benefit obligation is not reported on the financial statements and does not impact other comprehensive income.