Write down all the subsets of the following set: $\{a, b\}$

Let the set $C = \{(x, y) \mid x^2 - 2^y = 2023, x, y \in \mathbb{N}\}$. Then $\sum_{(x, y) \in C} (x + y)$ is equal to

Make correct statements by filling in the symbols $\subset$ or $\not\subset$ in the blank spaces:
${2,3,4} \dots {1,2,3,4,5}$

Examine whether the following statement is true or false:
$\{a\} \in \{a, b, c\}$

Make correct statements by filling in the symbols $\subset$ or $\not\subset$ in the blank spaces:
$\{ x:x \text{ is a student of class } XI \text{ of your school} \} \dots \{ x:x \text{ is a student of your school} \}$

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