From the following select which statement is true

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 $\frac{1}{2}$ 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 $L,$

$\frac{1}{2}L$ 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.