You need to meet the technical requirements for the site links.

Site, subnet, and site-link objects are stored in the Configuration partition, which replicates to every domain controller in the forest but is administratively owned by the forest root domain. By default, only members of Enterprise Admins and members of the Domain Admins group of the forest root domain (contoso.com in this forest) have permissions to modify objects in the Configuration container, including editing a site link ' s replication schedule. Admin1 is a member of Contoso\Enterprise Admins and therefore has forest-wide rights over the Configuration partition. Admin2 is a member of Contoso\Domain Admins; because contoso.com is the forest root domain, this group also carries default rights over the Configuration and Schema partitions. Admin3, however, is a member of Canada\Domain Admins, the Domain Admins group of the canada.contoso.com child domain, which has no inherent rights over the Configuration partition. Consequently, to change the replication schedule on all site links to 30 minutes, only Admin1 and Admin2 currently have the necessary permissions, making option C the correct answer.