In the mid 1960s, life insurance companies were signing up individuals for life insurance policies. A feature often included in the policies was the right to borrow against the cash value of the policy at a fixed rate of interest, say 8 percent. At the time, with interest rates of 3 to 4 percent, this feature didnt seem important. However, this feature proved extremely valuable to the insured, when interest rates soared to double digits in the early 1980s. Suddenly, the baby boomers were able to borrow at 8 percent and invest at 12 percent, while the insurance companies had to borrow at rates higher than 8 percent in order to honor their contracts. Many insurers were threatened with insolvency because of this feature in their contracts.

What is the underlying asset for the options in this real-life example?