What would your reply be?

You work as the network administrator at Domain.com. The Domain.com network consists of a single Active Directory domain named Domain.com. Domain.com has its headquarters located in London and branch office located in Paris. All servers on the Domain.com network run Windows Server 2008 and all client computers run Windows Vista.
Domain.com currently makes use two computers named CERTKILLER-SR01 running the DNS service configured as a primary master and CERTKILLER-SR02 configured as a secondary master for the Domain.com zone. A network user named Rory Allen wants to know which part of the DNS zone would be used to establish whether or not zone data has changed.
What would your reply be?

A.
You should inform Rory Allen that the secondary master would use the serial number.

B.
You should inform Rory Allen that the secondary master would use the database record tombstone.

C.
You should inform Rory Allen that the secondary master would use the TTL, or time to live.

D.
You should inform Rory Allen that the secondary master would use the NS record.

Explanation:
The serial number is utilized by secondary servers to establish whether or not the zone data has changed. This value is routinely updated with Windows Server 2008 DNS server by default. The zone’s TTL is used to verify what time to query for an update of the zone file from the master server except if a Notify message has been sent by the master server in the interim.