Question $6.(2+1+1+2$ points$)($a$)$ Describe the differences between the two classes of languages P and NP$,$ and tell the relationship between them. Answer: $($b$)$ Yes $($Yes $/$ No $/$ Unknown$).($c$)$ NO $($Yes $/$ No $/$ Unknown$).($d$)$ Show that DOUBLE$-$SAT is in NP$.$