History has shown that a market sell-off is a great time to add quality companies to your portfolio. Although no one can predict when that will happen, a 10% drop occurs about once every two years. That's why I'm highlighting five high-quality companies to buy if the most recent swoon persists.I can't tell you where Adobe,Markel,Take Two Interactive Software,Vertex Pharmaceuticals, and BostonBeerwill trade next week or next month. But I'm confident they will significantly outperform the market o