What universal set $(U)$ would you propose for the set of right triangles?

Make correct statements by filling in the symbols $\subset$ or $\not\subset$ in the blank spaces:
${ x:x \text{ is an equilateral triangle in a plane} } \dots { x:x \text{ is a triangle in the same plane} }$

Let $A = \{1, 2, \{3, 4\}, 5\}$. Is the statement $\{3, 4\} \in A$ correct or incorrect? Explain.

If $A = \{1, 2, 3, 4, 5, 6\}$, then which of the following is not true (in $in A$)?

Given the sets $A = \{1, 3, 5\}$,$B = \{2, 4, 6\}$,and $C = \{0, 2, 4, 6, 8\}$,which of the following sets can be considered as a universal set for all the three sets $A$,$B$,and $C$?
$X = \{0, 1, 2, 3, 4, 5, 6\}$

If $A = \{2, 3, 4, 5, 6\}$,then which of the following statements has a truth value of 'false'?