Which of the following is the purpose of a subnet mask in a network? (Select all that apply) a. A subnet mask is not necessary when a default gateway is specified. b. A subnet mask is used to differentiate between the network address, the host addresses, and the broadcast address. c. A subnet mask is required only when bits are borrowed on a network. d. A subnet mask is used to determine in which subnet an IP address belongs. e. A subnet mask is used to separate the 48-bit address into the OUI and the vendor serial number.