X-Men: Days Of Future Past Includes Nudity According To MPAA Rating

X (MPAA), Rating System Wiki

The Brief and Scandalous History of the X Rating

RetroNewsNow on X: 🎬On November 1, 1968, the Motion Picture Association of America's film rating system was officially introduced with the ratings G, M, R and X / X

X 18+ - Wikidata

MPAA Rating Bumper Rated X Remake (1970-1971) by TheAnthonyCorp on DeviantArt

What makes a movie X rated? - Quora

A History of the X and NC-17 Ratings – The Hollywood Reporter

What happened to the X Rating?

Which is worse, rated R or MA? - Quora

Saw X - Rotten Tomatoes