Final answer:
To join an 802.1x authenticated wireless network, the device Juan is configuring must run a supplicant agent. So, the correct option is A. Supplicant.
Step-by-step explanation:
Juan is configuring a new device to join his organization's wireless network, which uses 802.1x authentication. In an 802.1x network infrastructure, there are typically three components involved in the authentication process: the supplicant, the authenticator, and the authentication server.
In order for a device to join a wireless network using 802.1x authentication, a supplicant agent must be running on the device. The supplicant is responsible for sending authentication credentials to the authenticator on the network. The authenticator then forwards the credentials to the authentication server which verifies them and grants access to the network if they are valid. For a device to join this type of network, it must be running a supplicant agent, which is the component that resides on the client device and is responsible for providing credentials to the authenticator to gain access to the network. The authenticator acts as an intermediary, forwarding credentials to the authentication server, which then validates the credentials and either grants or denies network access.