Growth investors may be feeling worried about the 13.3% fall in the NASDAQ Composite Index last month, the worst decline since October 2008. But if you focus on business fundamentals, you’d notice that many companies are still posting healthy growth even as sentiment falters. And as famous investment guru Warren Buffett says — if the business does well, the stock price eventually follows. The key to doing well in investing is to focus on the stocks whose businesses are coasting along fine through both good times and bad. These are the businesses that you can count on to deliver superior returns in the long run. Let’s now turn our attention to four US growth stocks that could provide your investment portfolio with a strong boost. Mastercard (NYSE: MA) Mastercard is a global technology company in the payments space and serves as an important conduit between merchants and their customers to help facilitate secure and hassle-free payments....