$\begin{array}{l} A = \left\{ {{k^2} + 1|k \in \mathbb{Z},\left| k \right| \le 2} \right\}\\ \left| k \right| \le 2 \Leftrightarrow - 2 \le k \le 2\\ \Rightarrow A = \left\{ {5;2;1;2;5} \right\}\\ \Rightarrow A = \left\{ {5;2;1} \right\}\\ \Rightarrow 3\,\text{Phần tử} \to C \end{array}$