Which statement best describes why it was difficult for employees to obtain promotions according to Air Force Regulations and the course text?

Group of answer choices

a$.$ Commanders and supervisors are reluctant to create additional vacancies by promoting employees in existing positions.

b$.$ The burden of proof remains the employee$$s responsibility to show she or he meets the minimum standards for the grade or position.

c$.$ The Civil Service Commission had to review every promotion package to ensure commanders and supervisors followed all Commission policies and processes.

d$.$ Civilian personnel offices had to review promotion packages to ensure commanders and supervisors followed Civil Service Commission policies and processes.