Let L be a language recognizable by a finite automaton. The language
REVERSE (L) = {w such that w is the reverse of v where v ∈ L } is a
A.  regular language 
B.  contextfree language 
C.  contextsensitive language 
D.  recursively enumerable language 
Option: A Explanation : 
The grammars G = ( { s }, { 0, 1 }, p , s)
where p = (s —> 0S1, S —> OS, S —> S1, S —>0} is a
A.  recursively enumerable language 
B.  regular language 
C.  contextsensitive language 
D.  contextfree language 
Option: B Explanation : 
The logic of pumping lemma is a good example of
A.  pigeonhole principle 
B.  divideandconquer technique 
C.  recursion 
D.  iteration 
Option: A Explanation :
The pigeon hole principle is nothing more than the obvious remark: if you have fewer pigeon holes than pigeons and you put every pigeon in a pigeon hole, then there must result at least one pigeon hole with more than one pigeon. It is surprising how useful this can be as a proof strategy.
In the theory of formal languages in computability theory, a pumping lemma or pumping argument states that, for a particular language to be a member of a language class, any sufficiently long string in the language contains a section, or sections, that can be removed, or repeated any number of times, with the resulting string remaining in that language. The proofs of these lemmas typically require counting arguments such as the pigeonhole principle. So the answer is 'A'
