Answer
Check work for reasoning,
Work Step by Step
a) The limit as x approaches c does not exist since the one-sided limits are not equal.
b) Here the limit exists, but $f(c)$ is not defined and hence the function is not continuous.
c) The limit at $x=c$ exists but is not equal to $f(c),$ hence the function is not continuous.
d) The limit at $x=c$ does not exist because the one-sided limits are not equal.
