Investing.com - The next two months will be key for stocks, according to Bank of America Merrill Lynch (NYSE:BAC). In a note to clients, the Wall Street firm says investors should consider selling any rally in stocks if two events do not take place by the end of the third quarter.The first is new highs for the S&P 500.The second is a rebound in the hard-hit Chinese stock market, after the government's recent stimulus measures.BAML says it is worried by the fact that the yield on the 10-year note -- a key economic barometer -- cannot hold above 3%, despite a wealth of positive indicators, such as record corporate profits and a rock-bottom unemployment rate.The S&P 500 is about 2% below its record high of 2872.87, after suffering a 10% correction in February.