Answer
(a)
Work Step by Step
Since the quotient law is $$
\lim _{x \rightarrow c} \frac{f(x)}{g(x)}=\frac{\lim _{x \rightarrow c} f(x)}{\lim _{x \rightarrow c} g(x)}
$$
then it does not hold if the limit of the denominator is zero. That is, (a) is the correct answer.
