Here T -> XTX since T -> X and X->b S ->XbX since X->a S->aba
So,why is option 3 not accepted ?
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Read the question again, this time focus better. Take the grammar of the question, not the grammar in your mind.
I only need to see the rules for S to know that the strings in (3) are not part of the language.
S is the start symbol. Look at the rules for S. Think why I'm saying that aba and aa cannot possibly be in the language, without me having to look at any other rules whatsoever. You should be able to say "Looking at the rules for S, it is obvious that all strings in the language either xxx or yyy".