Q: To fill in the blank using (element of, not element of, is a subset of, is not a subset of).

{-1,-4} ___ {x N(natural numbers)/ (x+1)(x+5)(x-1) = 0}

{12} ___ {3k/ k N(natural numbers)}

{{12,13}} ___ {{12,21}, {12,13}, {-12,24}}

12 ____ {0, 12, 16, 23}

{a} ___ {{x}, {b}, {a,c,m}}