A. for all person x der exist a job y or (let another) job z is not same as job y then x shouldn't has job z.
Let y!= z and x dont have any job then also A returns true.
B. Returns true if y!=z and x has both jobs y as well as z.
C. If z=y it will return false.
D. if z=y then ~J(x,z) otherwise no problem.
D is correct.