A famous bit on Sacha Baron Cohen's Da Ali G Show had the clueless character pitch a literary agent "a book version of The Lord of the Rings" movies. However, a new survey shows a lot of folks don't know at least two popular movies that were once books.

Seventy-percent of those polled by ThriftBooks didn't know that Mean Girls and Die Hard were both books before hitting the big screen: Mean Girls was adapted from Rosalind Wiseman's 2002 work Queen Bees and Wannabes, while Die Hard was born from Roderick Thorp's 1979 page-turner Nothing Lasts Forever.

The survey of 2,000 American book readers revealed 67% preferred the book version to the movie from which it's adapted, but half of those polled say they prefer to watch a movie first, then pick up its original source.

Respondents don't mind changes to a story if it improves a movie -- but they find straying more than 23% from a source to be a "nuisance."

The biggest gripe readers have is when a movie's character drifts too far from their depiction in books -- looking at you, Tom Cruise in Jack Reacher -- with 52% saying that's the most bothersome; 27% don't like it when a movie changes a book's ending.

The poll also looked into holiday stories, with respondents saying a movie should only be dubbed a "Christmas movie" if there are "Christmas-related characters" or if the movie, "takes place during the season."

Tim Burton's Nightmare Before Christmas made the cut with 41% of those polled, more than the 26% who celebrate the holidays with Bruce Willis' John McClane, and the 20% who say Trading Places is a Christmas must-watch. Tom Hanks and Meg Ryan's You've Got Mail also made that list, according to 14% of those polled.

Survey questions, methodology and results have not been verified or endorsed by ABC News or The Walt Disney Company.

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