Your company has a single active directory forest that has an active directory domain named na.contoso.com. a member server named server2 runs the DNS server role. The server2 DNS service hosts multiple secondary zones including na.contoso.com. you need to reconfigure server2 as a caching-only DNS server. What should you do?（）
- AUninstall and reinstall the DNS service on server2.
- BChange all the DNS zones on server2 to stub zones.
- CDisable and then enable the DNS service on server2.
- DDelete the na.contoso.com DNS zone domain from server2. Restart the DNS service on server2.