Answer:
a. Cournot oligopoly.
The largest and probably most powerful cartel in the world, the OPEC (Organization of the Petroleum Exporting Countries), is an example of a Cournot oligopoly. In a Cournot oligopoly, the competing firms decide how much output they will produce. In the case of OPEC, the competing countries decide total output.
b. Stackelberg oligopoly.
The smartphone industry is a clear example of a Stackelberg oligopoly where Apple is the leader and the rest follows. In a Stackelberg oligopoly, the leader establishes output and/or price decisions and the rest follow.
c. Bertrand oligopoly.
The soda industry is an example of a Bertrand oligopoly where Coke is the leader and Pepsi follows. Even thought they control around 70% of the soda markets, they continuously fight and compete against each other, This industry cannot be considered a Cournot oligopoly since price is a major factor in the competition.
