Wall St. falls in broad selloff; Twitter tumbles; Ukraine Weighs

``Twitter shares tumbled 17.8 percent to $31.85 after the expiration of a six-month "lock-up" period that had restricted the sale of about 82 percent of its outstanding stock.. Traders also kept an eye on developments in Ukraine ... "The short-term issue is Ukraine. We don't know when we'll wake up one morning and (Russian President Vladimir) Putin is going to be in eastern Ukraine," said Jack De Gan, chief investment officer at Harbor Advisory Corp in Portsmouth, New Hampshire.''