Final answer:
The best-known marketing manifestation of selectivity and concentration is the creation of a strong brand name through significant advertising and marketing efforts, as seen with brands like Coca-Cola and Pepsi.
Step-by-step explanation:
According to the text, the best-known marketing manifestation of selectivity and concentration is the focus on creating a strong, recognizable brand name through substantial advertising efforts. This practice is exemplified by companies like Coca-Cola and Pepsi, which have established prominent brand names that are difficult for competitors to rival. This branding strategy is often pursued by firms that have reached a certain size, allowing them to invest significantly in marketing and advertising to create a differentiated product that stands out in an oligopolistic market.