Name The Year: Mexico sells U.S. Texas, California, New Mexico and Arizona.?

Questions

Furry, omnivorous american mammals each with a ringed bushy tail and dark stripe across the face?

Trespassing animals disliked by Betsy in Dickens David Copperfield?

An object hard to find because it is hidden by many other similar objects?

Comic opera by Gilbert and Sullivan, the only one of their opera that is sung through out?

Words used to identify people, places or things?