Vidal is an employee of Wild Thing Ranch. Vidal learns that Wild Thing is illegally importing endangered animals to sell as pets. He reports his employer’s illegal activities but is laid off shortly thereafter and successfully sues Wild Thing for retaliatory discharge. With respect to the employment-at-will doctrine, this is​
a. ​an exception based on public policy.
b. ​an exception based on tort theory.
c. ​an exception based on contract theory.
d. ​an example of the doctrine.