What type of policy states that certain events must happen before it becomes enforceable?

The correct choice is conditional because a conditional policy specifies that certain conditions or events must occur for the policy to be effective or for benefits to be paid out. These conditions typically relate to the insured's actions or the occurrence of specific risks outlined in the policy. For instance, a life insurance policy may require the policyholder to make premium payments regularly for the policy to remain in force or for a claim to be payable upon death. This concept is crucial in insurance because it directly ties the insurer’s obligations to the fulfillment of these specified conditions.

The other types of policies listed have different defining characteristics. A unilateral policy involves only one party (the insurer) making a guarantee or promise, while an adhesion policy is one that is drafted by one party (the insurer), and the other party (the insured) must accept the terms without negotiation. A reinstatement policy refers to the process of restoring a lapsed insurance policy once certain conditions are met, usually involving back premium payments, but does not inherently define any specific events that must occur for the policy to become enforceable in the same way that a conditional policy does.