What underlying database does microsoft use that enables active directory to use a directory tree structure?

It uses (Lightweight Directory Access Protocol) LDAP. LDAP which is a product of Internet Engineering Task Force defines how servers and clients exchange information about a directory. It runs directly over TCP/IP and UDP and is the most common way of interacting with the Active Directory.

answer

it would be true.

the today function returns a valid value without any arguments.

the today function returns the current date based on the computer's date setting and formatted as a date. today takes no parameters, but requires that you use empty parentheses