Final answer:
The appropriate completion for the sentence is 'changed;'. The past participle 'changed' correctly indicates a completed action, and the semicolon is used to join two closely related independent clauses.
Step-by-step explanation:
The correct option to complete the sentence is: The policy has changed; it's no longer applicable to this issue.
This sentence requires an appropriate verb form to indicate that the policy has undergone a change. The correct verb tense here is the past participle changed because the sentence is describing an action that has been completed in the past. Additionally, the use of the semicolon (;) is appropriate in this sentence as it is used to join two independent clauses that are closely related in thought and the second clause provides additional information about the first. The semicolon is a stronger division than a comma but less final than a period.