<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def subscription_path(cls, project, incident, subscription):
 """Return a fully-qualified subscription string."""

        return google.api_core.path_template.expand(
            "projects/{project}/incidents/{incident}/subscriptions/{subscription}",
            project=project,
            incident=incident,
            subscription=subscription,
        )