$L = \{ 0^{n+m }1^{n+m} 0^m \mid n, m \geq 0 \}$
The above language is
(a) CFL but not Regular
(b) CSL but not CFL
(c) RE but not CSL
(d) None of the above
I thought the answer would be (b) CSL but not CFL but it was given as (c) RE but not CSL
Can anyone explain how?