Which of the following statements is true?

a. Available for sale securities are securities bought and held primarily for sale in the near term to generate income on short-term price differences.

b. Trading securities and available-for-sale securities are classified as current or noncurrent assets depending on the circumstances.

c. Unrealized holding gains and losses are recognized in income for trading securities.

d. Companies may report changes in the fair value of available-for-sale securities in income before the security is sold.