The correct answer is B.
OBJ-2.1: The lightweight directory access protocol (LDAP) is a protocol used to access and update information in an X.500-style network resource directory. LDAP uses port 389. The service location protocol (SLP) is a protocol or method of organizing and locating the resources (such as printers, disk drives, databases, e-mail directories, and schedulers) in a network. This is an alternative protocol to LDAP in newer networks. SLP uses port 427. The remote desktop protocol (RDP) is a protocol used for the remote administration of a host using a graphical user interface. RDP operates over TCP port 3389. The domain name system (DNS) protocol is the protocol used to provide names for an IP address based on their mappings in a database using TCP/UDP port 53.