Final answer:
The computers in a local area network (LAN) are usually connected to the network via a hardware component called an adapter card.
Step-by-step explanation:
The correct answer is b. adapter card.
An adapter card, also known as a network interface card (NIC), is a hardware component that allows computers to connect to a local area network (LAN) or other networks. It is responsible for facilitating the transmission and reception of data between the computer and the network.
For example, if a computer is connected to a LAN via Ethernet, it would require an Ethernet adapter card to establish a connection with the network.