China’s stocks tumbled the most since the depths of a $5 trillion plunge in August as some of the nation’s largest brokerages disclosed regulatory probes, industrial profits fell and two more companies said they’re struggling to repay bonds. The Shanghai Composite Index sank 5.5 percent, with a gauge of volatility surging from the lowest level since March. Citic Securities Co. and Guosen Securities Co. plunged by the daily limit in Shanghai after saying they were under investigation for alleged rule violations. Haitong Securities Co., whose shares were suspended from trading, is also being probed. Industrial profits ... (full story)