What is the main function of the data link layer?

a$.$ It ensures that packets are transmitted in sequence

b$.$ It ensures error$-$free transmission between adjacent nodes in a LAN

c$.$ It ensures that there is a direct path between source and destination hosts in a WAN

d$.$ It ensures that both hosts in a LAN are using the same method of transmission $($simplex$,$ half duplex, or full duplex$)$ ear my choice