Question

Which of the following is not context free?

(a) {w: nA=nB=nC}

(b) {a*b*c*}

(c) {a^100b^100}

(d) All of the mentioned

I have been asked this question in a national level competition.

This interesting question is from Intersection with Regular Languages in section Properties of Context Free Languages of Automata Theory

Answer 1

Right choice is (d) All of the mentioned

To explain I would say: {a*b*c*} and (c) are regular languages while option (a) is not context free language.