When a Wireless LAN User goes from Access Point A$$s range into Access Point B$$s range, what does it do automatically to maintain network connectivity?

c$.$ Reestablish its connection with access point A on another channel

b$.$ Nothing because the Wireless LAN User will automatically associate with access point B

d$.$ Nothing; the user must reestablish network connectivity manually

a$.$ Associate with access point B in order to communicate with access point A