Asuite of three production servers that were originally configured identically underwent the same vulnerability scans. however, recent results revealed the three servers has different critical vulnerabilities. the servers are not accessible by the internet, and av programs have not detected any malware. the servers' syslog files do not show any unusual traffic since they were installed and are physically isolated in an off-site datacenter. checksum testing of random executables does not reveal tampering. which of the following scenarios is most likely:
a. servers have not been scanned with the latest vulnerability signature. b. servers have been attacked by outsiders using zero-day vulnerabilities. c. servers were made by different manufacturers. d. servers have received different levels of attention during previous patch management events.