Major averages recovered from a morning slump Thursday, ending mixed and mostly unchanged. The Nasdaq climbed 0.2% after falling as much as 1.2% early. The S&P 500 was flat, and the Dow lost less than 0.1%. Preliminary data showed NYSE and Nasdaq volume coming in slightly lower than Wednesday. The European Central Bank voted to leave interest rates unchanged, and chief Mario Draghi said the ECB will buy assets for at least two years.