The influence of advertising is felt in every phase of American life. The advertiser made the cigarette synonymous with masculine virility and suave sophistication. He gave birth to the multi-million dollar chewing gum industry by promising to double the public's pleasure and fun. Brand names for toothpastes, soaps, detergents, and deodorants have, through his efforts, become household expressions. Perhaps a public service was performed when advertisers were asked to convince the American public that it should eat horse mackerel. The advertising industry met this challenge by changing the horse mackerel's name to tuna fish.

Q. Underline the key word in the topic sentence.