Which of the following ensures that a function $f$ is continuous at -6?

(a) $\displaystyle \lim_{x \to -6} f(x)$ exists.
(b) $f(-6)$ exists.
(c) $\displaystyle \lim_{x \to -6} f(x)=f(-6)$.
(d) All of the above.
(e) None of the above.

Answer: