What universal set $(s)$ would you propose for each of the following :

The set of right triangles

List all the elements of the following sers :

$C = \{ x:x$ is an integer ${\rm{; }}{x^2} \le 4\} $

Make correct statements by filling in the symbols $\subset$ or $ \not\subset $ in the blank spaces:

$\{ x:x$ is an even natural mumber $\}  \ldots \{ x:x$ is an integer $\} $

Let $A=\{1,2,3,4,5,6\} .$ Insert the appropriate symbol $\in$ or $\notin$ in the blank spaces:

$ 2 \, ....... \, A $

Write the following sets in roster form :

$C = \{ x:x{\rm{ }}$ is a two-digit natural number such that sum of its digits is $8\} $

For an integer $n$ let $S_n=\{n+1, n+2, \ldots \ldots, n+18\}$. Which of the following is true for all $n \geq 10$ ?