If A, B, C are three non empty sets such that $A\subset B\subset C$ , then

A,B,C are non empty sets, Let $A=\left\{1,2,3\right\},B=\left\{1,2,3,4\right\},C=\left\{1,2,3,4,5\right\}$

and given $A\subset B\subset C$

A) $\left(A\cap B\right)\cap C=A$

$\left(A\cap B\right)\cap C=\left\{1,2,3\right\}\cap \left\{1,2,3,4,5\right\}$

$\left(A\cap B\right)\cap C=\left\{1,2,3\right\};\left(A\cap B\right)\cap C=A$  it is the common sets

B) $\left(A\cup B\right)\cup C=C$

$\left(A\cup B\right)\cup C=\left\{1,2,3,4\right\}\cup \left\{1,2,3,4,5\right\}$

$=\left\{1,2,3,4,5\right\}$

$\left(A\cup B\right)\cup C=C$ . If is the common set

$A^{|}=\mu -A$

$=\left\{4,5,6\right\}$

$B^{|}=\mu -B$

$=\left\{5,6\right\}$

$C^{|}=\mu -C$

$=\left\{6\right\}$

$A^{|}\supset B^{|}\supset C^{|}$  It is the correct formula