【单项选择题】
Which statement about WSA user authentication is true?() 
A、A. a single WSA can have multiple LDAP realms
B、B. WSA supports LDAP but not NTLM
C、C. WSA supports NTLM but not LDAP
D、D. a single WSA can have up to two authentication realms: one for LDAP and for NTLM