Let $A$ be an $m \times n$ matrix. Suppose that $C=\left(\begin{array}{l}A \\ B\end{array}\right)$ is an $(m+k) \times n$ matrix whose first $m$ rows are the same Pagenose of $A$. 79 fove that ker $C \subseteq$ ker $A$. Thus, appending more rows cannot increase the size of a matrix's kernel. Give an example in which $\operatorname{ker} C \neq \operatorname{ker} A$.