Answer:
From the given machine it is clear that λ is accepted because initial state S is final state. Now by input ‘ab’ we reach another final state B and by input ‘aba’ we reach another final state C.
So, we can also get final state by the combination of input ‘ab’ and ‘aba’.
Regular Expression RE = (ab + aba)*
But here a and c is correct answer.
Because (ab + aba)* = (ab + aba + abab)*
Both are equivalent because as we know,
(a + b)* = (a + b + ab)* = (a* + b)* = (a + b*)* = (a + b*)* = (a*b*)*
If we calculate the regular expression of final state it will be (λ + ab + aba + abab + abaab)*
So, overall we can say it (ab + aba)*
So, answer is a. and though a. and c. is same so, answer is a. and c.