Complex sentence: Gray Tuesday occurred on February 27th, 2007 when the Chinese stock market declined 8.8%, the largest drop in 10 years, when Deng Xiaoping's death led to an 8.9% drop in stocks.
Split into simpler sentences: Gray Tuesday occurred on February 27,2007 when the Chinese stock market declined 8.8%. This was the largest drop since Deng Xiaoping's death on February 19,1997, which led to an 8.9% drop in stocks.