Find a$)$ any critical values and b$)$ any relative extrema.

$g(x)=x^3-27x63$

a$)$ Select the correct choice below and, if necessary, fill in the answer box within your choice.

A$.$ The critical value$($s$)$ of the function is$/$are $.$

$($Use a comma to separate answers as needed.$)$

B$.$ The function has no critical values.