Decide,among the following sets,which sets are subsets of one another:
$A = \{ x: x \in \mathbb{R} \text{ and } x \text{ satisfies } x^2 - 8x + 12 = 0 \},$
$B = \{2, 4, 6\}, C = \{2, 4, 6, 8, \dots\}, D = \{6\}$

(D) Given $A = \{ x: x \in \mathbb{R} \text{ and } x^2 - 8x + 12 = 0 \}$.
Solving the quadratic equation $x^2 - 8x + 12 = 0$:
$(x - 2)(x - 6) = 0$,which gives $x = 2$ or $x = 6$.
Thus,$A = \{2, 6\}$.
Given sets are $B = \{2, 4, 6\}$,$C = \{2, 4, 6, 8, \dots\}$,and $D = \{6\}$.
Comparing the elements:
$D = \{6\} \subset A = \{2, 6\}$.
$A = \{2, 6\} \subset B = \{2, 4, 6\}$.
$B = \{2, 4, 6\} \subset C = \{2, 4, 6, 8, \dots\}$.
Therefore,the subset relations are $D \subset A \subset B \subset C$.