Question

Which of the following represents a language which has no pair of consecutive 1’s if ∑= {0,1}?

(a) (0+10)*(1+ε)

(b) (0+10)*(1+ε)*

(c) (0+101)*(0+ε)

(d) (1+010)*(1+ε)

I got this question in a national level competition.

My question is based upon Building Regular Expressions topic in chapter Regular Expressions and Languages of Automata Theory

Answer 1

Correct choice is (a) (0+10)*(1+ε)

The best I can explain: All the options except ‘a’ accept those strings which comprises minimum one pair of 1’s together.