A DNS server is configured as a secondary server and successfully synchronizes with the primary server when the secondary server is first started. A zone file on the primary server is updated but the secondary server fails to synchronize. The secondary server is rebooted but this fails to help. Which failure caused this problem?
failure to update the NS record of the updated zone file
failure to update the time stamp of the updated zone file
failure to update the serial number of the updated zone file
failure to update the SOA ttl number of the updated zone file