You are a network administrator for your company. The network consists of a single Active Directory domain. The company has offices in 25 cities. Each office is configured as a single site. You are responsible for one site that is configured as shown in the exhibit. （Click the Exhibit button.） An IP site link connects your site and the site at the company’s main office. The company replaces your router with a firewall device. The firewall is configured to allow HTTP， SMTP， FTP， NNTP， global catalog queries， and VPN packets to pass. You discover that replication with other sites is not occurring. You need to ensure that you can replicate with other sites. You need to achieve this goal without removing or reconfiguring the firewall.  What should you do？ （）

• A、 Create a new SMTP site link between your site and each of the other sites.
• B、 Configure one domain controller in your site as a global catalog server.
• C、 Configure both domain controllers in your site to use a fixed port when replicating.
• D、 Create a VPN between your site and the site at the main office.