Explanation/Reference:
Explanation:
An X.509 certificate contains information about the identity to which a certificate is issued and the identity that issued it. Standard information in an X.509 certificate includes:
Version - which X.509 version applies to the certificate (which indicates what data the certificate must

include)
Serial number - the identity creating the certificate must assign it a serial number that distinguishes it

from other certificates
Algorithm information - the algorithm used by the issuer to sign the certificate

Issuer distinguished name - the name of the entity issuing the certificate

Validity period of the certificate - start/end date and time

Subject distinguished name - the name of the identity the certificate is issued to

Subject public key information - the public key associated with the identity

Extensions (optional)

Incorrect Answers:
B: The telephone number of the department is not included in an X509 certificate.
C: The secret key of the issuing CA is not included in an X509 certificate. The secret key is the private key which is never distributed.
D: The key pair of the certificate holder is not included in an X509 certificate. A key pair includes a private key which is kept private.
References:
http://searchsecurity.techtarget.com/definition/X509-certificate