“Avatar” continues to gain Oscar momentum with a nomination for the Writers Guild of America Awards — this despite complaints that James Cameron’s screenplay is filled with cheesy dialogue and is derivative of “Pocahontas” and numerous other films. The other nominees for best original screenplay are “(500) Days of Summer,” “The Hurt Locker,” “A Serious Man” and “The Hangover.” The best adapted screenplay nominees are “Up in the Air,” “Crazy Heart,” “Precious,” “Julie & Julia” and “Star Trek.” The WGA announced last week that it had disqualified “Up,” “Inglourious Basterds,” “An Education,” “District 9,” “In The Loop,” “Fantastic Mr. Fox,” “A Single Man” and “The Road,” mostly over guild membership issues.