From the following select which statement is true

Question $1$Answer

a$.$

Some non$-$regular languages can be converted to regular languages by removing finitely many strings

b$.$

In Assignment $1$ you showed that the operator $1/2$ is closed with respect of regular languages. Then we can conclude this operator is also closed with respect to non$-$regular languages, since for any nonregular language L$,1/2$L must be non$-$regular, otherwise L would be regular as well, which is a contradiction.

c$.$

Any NFA can be used to define a context$-$free grammar.

d$.$

Context$-$free grammars can generate only non$-$regular languages.