Answer: The lower bound of a put option

**Explanation:** The correct answer is **A** because the lower bound of a put option is defined as the greater of zero or the present value of the exercise price minus the spot price. This is because the buyer of a put option will only exercise the option if the spot price at maturity is below the exercise price. The exercise price, therefore, serves as the upper bound on the value of the put option. - **Option B** is incorrect as it describes the lower bound of a call option, which is the underlying's spot price minus the present value of the exercise price or zero, whichever is greater. - **Option C** is incorrect as it refers to the upper bound of a put option, which is not relevant to the given question.

Author: LeetQuiz Editorial Team