The correct answer is: C. a cartel
A cartel is a formal agreement among competing firms to fix prices, limit production, or share markets. Cartels are illegal in most countries, but they can be very profitable for the firms involved.
A non-collusive oligopoly is an oligopoly in which the firms do not cooperate with each other. In a non-collusive oligopoly, each firm acts independently and tries to maximize its own profits. This can lead to a situation where the firms produce too little output and charge too high prices.
Price leadership is a situation in which one firm in an oligopoly sets the price for the industry, and the other firms follow. Price leadership can be either explicit or implicit. Explicit price leadership occurs when the leading firm announces its price and the other firms follow. Implicit price leadership occurs when the leading firm sets a price and the other firms simply match it.
A concentrated industry is an industry in which a small number of firms have a large share of the market. Concentrated industries are often characterized by oligopoly or monopoly.
In conclusion, a group of firms that gets together to make price and output decisions is called a cartel.