Every regular expression can be expressed as a context$-$free grammar. That is$,$ for every regular expression, there is a context$-$free grammar that has the same language as the regular expression.

Your friend says the regular expression $(0^10^)0^$

can be generated by the context$-$free grammar: S$0$S$01$S$1$

But the language of the regular expression and the language of the CFG are not the same!

Which of the following strings do match the regular expression but cannot be generated by the context$-$free grammar?

Choice $1$ of $7$:$0$

Choice $2$ of $7$:$10$

Choice $3$ of $7$:$00$

Choice $4$ of $7$:$111$

Choice $5$ of $7$:$0110$

Choice $6$ of $7$:$00100$

Choice $7$ of $7$:The grammar can generate any string that the regular expression matches.