A realization event occurs:

		a. when the value of stock which an individual holds at year-end increases.
		b. when a leasehold terminates and the property along with improvements made by the lessee revert back to the ownership of the lessor, as required by Helvering v. Bruun.
		c. when a market transaction takes place with another party that alters the taxpayer's mix of assets and liabilities and results in a change in net worth.
		d. All of the above.