It’s a moment of truth for Facebook as shareholders evaluate whether to sell 271 million shares Thursday, as the first of several lockup period expires. That adds up to ten percent of shares outstanding.

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The big question: Will a flood of shares send the stock even lower? But with shares off 45 percent since its May IPO, some say it may not have much further to fall. (Related: Why Facebook Shares Won't Fall After the Lock-Up.)