Based on the IEEE $802$ reference model, the correct order for data encapsulation for the units $($Segments$,$ Bits, IP datagrams, LLC$-$PDU, Data, MAC frames$)$ is:

a$.$ Data, Segments, IP datagrams, LLC$-$PDU, MAC frames, Bits

b$.$ Data, Segments, MAC frames, IP datagrams, LLC$-$PDU, Bits

c$.$ Data, IP datagrams, MAC frames, Segments, LLC$-$PDU, Bits

d$.$ Bits, Segments, IP datagrams, MAC frames, LLC$-$PDU, Data