Question $6$

If a problem is NP$-$hard, what can be said about finding an efficient solution for it$?$ Select all that apply.

a$)$ It is at least as hard as any NP$-$complete problem.

b$)$ It always has a solution that can always be verified quickly.

c$)$ It can be solved in polynomial time if P $=$ NP$.$

d$)$ It is guaranteed to be solvable in exponential time.