The main purpose of the guaranteed insurability rider benefit is to give the policyholder the right to

Cancel a health-based exclusion after a symptom-free period
Include his parents under the policy
Increase cover when a key life event occurs
Maintain cover despite a fall in investment value

The correct answer is: C. Increase cover when a key life event occurs.

A guaranteed insurability rider is a type of rider that allows a policyholder to increase their life insurance coverage without having to provide evidence of insurability. This can be helpful if a policyholder’s health changes or if they experience a key life event, such as getting married, having children, or buying a home.

Option A is incorrect because a guaranteed insurability rider does not allow a policyholder to cancel a health-based exclusion after a symptom-free period. A health-based exclusion is a provision in a life insurance policy that excludes coverage for certain pre-existing conditions.

Option B is incorrect because a guaranteed insurability rider does not allow a policyholder to include their parents under the policy. A guaranteed insurability rider is a rider that allows a policyholder to increase their life insurance coverage, not to add additional people to the policy.

Option D is incorrect because a guaranteed insurability rider does not allow a policyholder to maintain cover despite a fall in investment value. A guaranteed insurability rider is a rider that allows a policyholder to increase their life insurance coverage, not to maintain their coverage if the value of their investments falls.