 Shares of Clean Energy Fuels Corp. dropped 8.8 in very active morning trading Thursday, after the provider of environmentally friendly fuel for the transportation industry disclosed that its largest shareholder reduced its stake by about 10.6 million shares. Trading volume swelled to 19.0 million shares, already more than the full-day average over the past 30 days of about 13.9 million shares, according to FactSet. 