$(8$ pts$)$ Consider the context$-$free grammar defined by:

$S$aSb$|bSa|aS|bS|lon$

I. Identify the variables, terminals, and start symbol of this grammar.

II$.$ Describe the language generated by this grammar.

III. Provide a derivation for the string "ababb".

IV$.$ Is the string "ababab" in the language? Justify your answer.