on a job description ,what is the difference between necessary skills and desirable skills

Question

a.necessary skills are those a person needs to work at a job,and desirable skills are those that a company hopes a candidate has
b.necessary skills are those a person will learn on the job,and desirable skills are those that will ensure eventual promotion
c.necessary skills are those a person must have to apply for the job ,and desirable skills are those that a company plans to train an employee to have

my answer is c

Answer 1

I disagree.

Answer 2

would it be b

Answer 3

no