Which of the Following Is Correct Regarding Seniority Provisions in Collective

Which of the following is correct regarding seniority provisions in collective agreements:

A) Seniority is a factor in all job-related decisions such as layoffs, unless the collective agreement provides otherwise.
B) There will be one seniority calculation for all seniority-related provisions in the collective agreement such as vacations and layoffs.
C) The collective may provide that the employee with the most seniority will be awarded a job vacancy provided that they have sufficient ability for the job.
D) Employers prefer seniority to be given more weight in job-related decisions.
E) Seniority is usually the sole factor used when employees apply for a job vacancy.