The string $1101$ does not belong to the set represented by
Only (a) and (b) can generate $1101$.
In (c) after $11$, we can not have $01$ and so $1101$ cannot be generated.
In (d) Every $11$ followed by $0$ and no single occurrence of $1$ is possible. So it cannot generate $1101$ or $11011$.
I think option (c) is more appropriate to choose from, because even option (d) can generate 11011 or 110110 in which 1101 is a substring.
yeahh. I think D is not allowed because let (00+(11)*0)* can be written as (a+b)*
and we know 'bb' is allowed in (a+b)* so in (00+(11)*0)* 110110110... is allowed. now see bold substring is 1101.
option d is quite inviting to choose it as we can have only even number of 1's with this regular set where as our original string contains 3 1's
from option c and d we can't generate string 1101.
therefore both c and d are correct
Here point to keep in mind is, question is asking string not substring, means given RE should not generate 1101 as string. If we look at option d, it will generate either no 1 or even no. of 1's always & can't generate odd no. of 1's. Hence D is the answer.
Thanks a lot