A Life insurance policy that provides protection for the insured's whole life with level premiums for a twenty-year period is:

Universal Life insurance provides flexibility in premium payments and death benefits, allowing policyholders to adjust these aspects over time. Unlike Limited Pay Life, Universal Life does not mandate level premiums for a defined twenty-year period but instead offers more freedom in managing policy features.

Variable Life insurance combines a death benefit with an investment component, allowing policyholders to allocate premiums into various investment options. This type of policy does not guarantee level premiums for a specific twenty-year duration, making it distinct from the described insurance arrangement.

Adjustable Life insurance permits policyholders to modify the policy's coverage, premiums, and death benefits as their needs evolve. While this type of policy offers flexibility similar to Universal Life, it does not align with the characteristic of maintaining level premiums for a twenty-year period as specified in the question.