These companies can all benefit from the long-term growth of AI spending.September is historically a bad month for stocks. The ninth month of the year is the only month when the historic average performance of each of the major stock indexes is a negative number.But if you have a long-term investing mindset, the September sell-off could present a great opportunity. Not only do the winter months bring historically strong returns, but any sell-off in stocks gives investors a chance to buy a stake in great com ...