Choose the best reason why the function $$f(x)=\left\lbrace \begin{array}{ll} -1-x, & \quad {\rm if}\quad x \le 7, \\ x^2-7 x, & \quad {\rm if} \quad x >7 \end{array} \right.$$ is discontinuous at $a=7$.

A. $\lim_{x\to a} f(x)\not = f(a)$

B. $\lim_{x\to a} f(x)$ doesn't exist.

C. The function is not defined at the point given.

Answer: