Which option is the code field of n EAP packet?

Which option is the code field of n EAP packet?
A . one byte and 1=request, 2=response 3=failure 4=success
B . two byte and 1=request, 2=response, 3=success, 4=failure
C . two byte and 1=request 2=response 3=failure 4=success
D . one byte and 1=request 2=response 3=success 4=failure

Answer: D