The subnet mask is used to determine the network and host portions of an IP address. It helps in defining the size of the subnet and the range of IP addresses within that subnet. * Subnet Portion: The subnet mask identifies which part of the IP address refers to the network (subnet) portion. * Host Portion: The remaining part of the IP address after applying the subnet mask identifies the specific host within the subnet. Options A and D are correct as they capture the details about the subnet and host portions of an IP address. Reference: Cisco DevNet Documentation: Understanding Subnetting