Complex sentence: In 1987, Coca-Cola once again became one of the 30 stocks which makes up the Dow Jones Industrial Average, which is commonly referenced as a proxy for stock market performance; it had previously been a Dow stock from 1932 to 1935.
Split into simpler sentences: In 1987, Coca-Cola once again became one of the 30 stocks which makes up the Dow, the Dow Jones Industrial Average, which is commonly referenced as the performance of the stock market. It had previously been a Dow stock from 1932 to 1935.