LONDON, Dec. 3 - The BBC, Britain's public service broadcaster, acknowledged Friday that it had been tricked into broadcasting an interview with a man pretending to be a spokesman for Dow Chemical, who claimed that the company had taken the blame for the disaster in Bhopal, India, in 1984. The hoax, contradicting Dow Chemical's rejection of any responsibility, came on the 20th anniversary of the catastrophe, when waves of lethal gas escaped from a chemical plant in Bhopal, in central India, killing more than 3,500 people and injuring thousands more. At the time, the plant was owned by the Union...