In a study analyzing employee performance, a n HR staffer conducts regression analysis with the variable "Job Category" coded as $1$ for junior, $2$ for mid$-$level, and $3$ for senior positions. The regression coefficients for these categories are found to be $00,20,$ and $30,$ respectively. What can be concluded from these coefficients?

Group of answer choices

A$.$ Mid$-$level is our base case for comparison

B$.$ Senior employees perform significantly better than junior employees.

C$.$ The effect of job category on employee performance is not significant.

D$.$ The regression model is invalid since job category is a categorical variable.